The attack that killed four Americans at the U.S. Consulate in Benghazi, Libya, apparently began as a spontaneous protest against an anti-Islam film before turning violent, Susan Rice, U.S. ambassador to the United Nations, said Sunday.

Rice, appearing in NBC’s “Meet the Press,” said she was citing preliminary information and that the FBI was investigating the Tuesday night attack that killed the U.S. ambassador to Libya, Chris Stevens, and three others.

A wave of protests and violence has swept across the Middle East and elsewhere in the Muslim world over an obscure, amateurish movie called "Innocence of Muslims" that depicts Muhammad as a fraud, a womanizer and a pedophile. Anti-U.S. protests in 20 countries led the Pentagon to dispatch elite Marine antiterrorism teams to Libya and Yemen and to position two Navy warships off Libya's coast.

Meanwhile, the State Department ordered all nonessential U.S. government workers and their families out of Sudan and Tunisia. In Lebanon, protesters torched an American fast-food restaurant. Even as tensions appeared to ease over the weekend, al-Qaida's most active Mideast branch was calling for further attacks on U.S. embassies.

"There's no question, as we've seen in the past with things like 'The Satanic Verses,' with the cartoon of the Prophet Muhammad, there have been such things that have sparked outrage and anger and this has been the proximate cause of what we've seen," Rice said.

“What happened in Benghazi was in fact initially a spontaneous reaction to what had just transpired hours before in Cairo, almost a copycat of the demonstrations against our facility in Cairo, prompted by the video,” Rice said.

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Protesters in Cairo had breached the walls of the U.S. Embassy and tore down the American flag.

In Benghazi, Rice told “Meet the Press” host David Gregory, “Opportunistic extremist elements came to the consulate as this was unfolding, they came with heavy weapons, which unfortunately are readily available in post-revolutionary Libya, and it escalated into a much more violent episode.”

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There was “no actionable intelligence” that the attack in Benghazi was imminent, Rice said. The attack overwhelmed security in place at the consulate, she said.

Rice’s comments came a day after Libyan President Mohammed Magarief told NBC News that “foreigners” were involved in the planning and execution of the attack.

He expanded on the assertion Sunday, saying on CBS’ "Face the Nation" that about 50 people, not all Libyans, have been arrested in connection with the Benghazi attack, which he said was planned by al-Qaida-linked foreigners, some from Mali and Algeria.

Magarief said there was little doubt the assault was planned rather than a spontaneous reaction to the video, as came on the 11th anniversary of the 9/11 terrorist attacks in the U.S.

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He said the security situation in Libya remained "difficult" for Americans, as well as for Libyans. The United States wants the FBI to investigate the consulate attack, but Magarief said it may be too soon to send in investigators.

"It may be better for them to stay away for a little while until we do what we have to do ourselves," he said.

Rice told "Meet the Press" that the U.S. is working with authorities in Libya, which has received $200 million in U.S. aid since 2011, to bring to justice those responsible for the attack.

This article includes reporting by Reuters.

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The bodies of four Americans killed in an attack on the U.S. Consulate in Benghazi, Libya, earlier in the week were returned to the United States and honored in a somber ceremony at Joint Base Andrews, Md., on Friday.

President Barack Obama arrived shortly before the transfer ceremony honoring the victims — U.S. Ambassador Chris Stevens, information management officer Sean Smith and security personnel Tyrone Woods and Glen Doherty.

Marines carried flag-draped coffins bearing the remains of the four across the tarmac and placed them before a gathering of family, friends, White House officials and high-level State Department personnel. In total, 800 to 1,000 were in attendance, an Air Force official said.

After a moment of silence and a prayer, Secretary of State Hillary Clinton eulogized each of the victims.

"We owe it to those four men to continue the long, hard work of diplomacy," Clinton said.

"May God bless them, and grant their families peace and solace, and may God continue to bless the United States of America," Clinton said, before making way for comments by Obama.

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The president said the men embodied and lived "the American ideal," embracing what he called "the fundamental American belief that we can leave this world a little better than before."

In honoring the fallen Americans, he also made a case for continued diplomatic and aid commitments to allies in the Middle East.

"Even as voices of suspicion and mistrust seek to divide countries and cultures from one another, the United States of America will never retreat from the world. We will never stop working for the dignity and freedom that every person deserves. ... That's the spirit that sets us apart from other nations. That was their work in Benghazi and this is the work we will carry on."

After the national anthem and a prayer, "America the Beautiful" was played as the caskets were loaded into waiting hearses, which then departed.

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Updated at 6:30 p.m ET: U.S. Muslims are seeing a spike in hate calls and are concerned about possible retaliatory attacks on domestic mosques following the fatal attack on the U.S. consulate in Libya and protests at the U.S. Embassy in Cairo.

“We’re starting to get hate calls and we’d already seen a wave of anti-Muslim incidents,” Ibrahim Hooper, spokesman for the Council on Arab-Islamic Relations in Washington, D.C., told NBC News on Wednesday.

“Our first thought is condemning the attacks. Obviously this is something we’re concerned about,” he said. Muslims are feeling insecure, he added.

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The Muslim civil rights group later Wednesday held a news conference to condemn the attacks in Libya and Egypt.

The U.S. ambassador to Libya and three embassy staffers were killed in the assault on the Benghazi consulate, which was stormed by Islamist gunmen. Another assault was mounted on the U.S. Embassy in Cairo.

On Tuesday, CAIR issued a statement urging Muslims to ignore the distribution of what it called the “trashy” anti-Islam film blamed by some for the attacks.

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Nihad Awad, executive director of CAIR, said:

"We urge that this ignorant attempt to provoke the religious feelings of Muslims in the Arabic-speaking world be ignored and that its extremist producers not be given the cheap publicity they so desperately seek. Those who created this trashy film do not represent the people of America or the Christian faith. The only proper response to intentional provocations such as this film is to redouble efforts to promote mutual understanding between faiths and to marginalize extremists of all stripes.”

On Wednesday, Awad said CAIR condemns the attacks in Libya and Cairo: "The actions of the attackers are totally inexcusable and un-Islamic."

An FBI spokesperson told NBC News on Wednesday that the agency has extensive nationwide community outreach through special agents and field offices to local Muslim communities.

Ambassador Stevens was 'courageous and exemplary,' Obama says

“We encourage anyone who thinks they are being threatened or intimated to contact us or law enforcement right away,” the FBI said.

In Rutherford County, Tenn., where the Islamic Center for Murfreesboro went through threats, attacks and a court fight to open last month, the sheriff’s office said on Wednesday it was unaware of any threats or protests following the Libya and Egypt attacks.

“We will respond to protect the Islamic Center,” sheriff’s spokesperson Lisa Marchesoni told NBC News.

Ossama Bahloul, the center's imam, told NBC News, that the center will continue to pay the overwhelming cost of security to protect the center "due to the past history of violence and threats that have been aimed at The Islamic Center of Murfreesboro along with the current concerns."

Bahloul also said the center "condemns in the strongest possible words" the killings in Libya and attack in Cairo.

The New York Police Department told NBC News that there was no new threat, but as a precaution it would ramp up security at numerous religious institutions, including Coptic Christian churches, synagogues and mosques.

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On Aug. 6, a mosque in Joplin, Mo., was burned to the ground. The same mosque was the subject of an attemped arson a month earlier.

In France, vandals smeared human feces on the doors of a mosque in Limoges sometime between Tuesday night and early Wednesday morning. There was no immediate indication, however, that the desecration was linked to the unrest over the film. The doors were daubed with neo-Nazi graffiti in July, news agencies said.

Hassan Shibly, executive director of the Florida Council on American Islamic Relations in Tampa, Fla., said if an attack on a mosque occurred it would be hard to know who would be retaliating against what.

“When somebody knocks on my door at CAIR, I just hope I don’t hear a gunshot," Shibly told NBC News. "There are a lot of crazies out there promoting hate.”

NBCNewYork.com's Jonathan Dienst and NBC News' Kari Huus and Jeff Black contributed to this article.

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J. Christopher Stevens, the U.S. Ambassador to Libya who was among four Americans killed amid protests in Libya, was a "courageous and exemplary representative of the United States," President Barack Obama said in a statement on Wednesday.

The four -- who also included Foreign Service Information Management Officer Sean Smith, a father of two -- "exemplified America's commitment to freedom, justice, and partnership with nations and people around the globe," Obama said.

Born in 1960 in northern California, Stevens had been a diplomat for two decades after previously working as an international trade lawyer in Washington, D.C., according to his biography on the State Department website.

"Chris was committed to advancing America's values and interests, even when that meant putting himself in danger," Secretary of State Hillary Rodham Clinton said Wednesday in a statement posted on the official Facebook page of the U.S. Embassy in Tripoli.

Ben Curtis / AP, file

U.S. envoy Chris Stevens speaks to local media at the Tibesty Hotel in Benghazi, Libya, in this Monday, April 11, 2011 file photo.

"I had the privilege of swearing in Chris for his post in Libya only a few months ago. As the conflict in Libya unfolded, Chris was one of the first Americans on the ground in Benghazi. He risked his own life to lend the Libyan people a helping hand to build the foundation for a new, free nation. He spent every day since helping to finish the work that he started."

Stevens had only just taken up his appointment, arriving in May after having served two previous roles in the country: Special Representative to the Libyan Transitional National Council during the Libyan revolution from March 2011 to November 2011, and Deputy Chief of Mission from 2007 to 2009.

US ambassador, 3 others killed in attacks on Libya mission

He had also previously worked in Jerusalem, Damascus and Riyadh and was a Pearson Fellow with the Senate Foreign Relations Committee. From 1983 to 1985 he taught English as a Peace Corps volunteer in Morocco.

A video posted on the U.S. Embassy's official YouTube channel in May showed Stevens introducing himself to the Libyan people and speaking of his excitement at his new role.

He was fluent in Arabic and French, and had earned an undergraduate degree at the University of California at Berkeley in 1982, a J.D. from the University of California's Hastings College of Law in 1989, and an M.S. from the National War College in 2010.

'Smiling, easygoing'
The Washington Post reported that Stevens was "smiling, easygoing and friendly" and "well-known at the State Department and on Capitol Hill."

His efforts to improve relations between the U.S. and Libya were underlined at one of his most recent public appearances. At a reception in Tripoli on August 26, he announced that the issuing of U.S. visas to Libyans would resume the following morning, according to a report in The Tripoli Post.

"The reopening of our consular section will create new opportunities for deepening the ties between our two countries," the newspaper quoted him as saying. "Relationships between governments are important, but relationships between people are the real foundation of mutual understanding," Stevens said.

A statement from Frank Wu, Chancellor and Dean of the University of California's Hastings College of the Law, issued to NBC Bay Area station KNTV, said: "The Ambassador was performing the highest role that a lawyer is called upon to perform: public service. He and I communicated when he was appointed Ambassador. He had been looking forward to sharing his experiences with students when he returned. This is a tragedy. We mourn this loss."

U.S. Senator Marco Rubio (R-FL), a member of the Senate Foreign Relations Committee and Select Committee on Intelligence, also issued a statement, saying: "I had the chance of meeting Ambassador Chris Stevens during his confirmation process and again when I visited Libya last year. He was an exemplary diplomat and his embassy staff could not have been more helpful and knowledgeable during my visit. My prayers are with the families and loved ones of these courageous diplomats who were working to help the Libyan people rise from the ashes of Gaddafi's rule."

Lara Friedman, director of policy and government relations at Israeli-American charity, Americans for Peace Now, who described herself as a friend of Stevens, posted on Twitter that his death was "incomprehensible, tragic."

The BBC reported that, in diplomatic cables leaked by the WikiLeaks site in 2010, Stevens had once described Col. Moammar Gadhafi as "notoriously mercurial" and wrote that he could be an "engaging and charming interlocutor."

Sean Smith was a husband and a father of two, who joined the State Department ten years ago, Clinton's statement said. "Like Chris, Sean was one of our best. Prior to arriving in Benghazi, he served in Baghdad, Pretoria, Montreal, and most recently The Hague," it said.

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