Discuss as:

Holder: US can legally kill Americans in terror groups

The U.S. government is legally justified in killing its own citizens overseas if they are involved in plotting terror attacks against America, Attorney General Eric Holder said Monday, offering the Obama administration's most detailed explanation so far of its controversial targeted killing program.

"In this hour of danger, we simply cannot afford to wait until deadly plans are carried out, and we will not," he said in remarks prepared for a speech at Northwestern University's law school in Chicago.

An American-born Islamic cleric, Anwar al Awlaki, was killed in a U.S. drone attack in Yemen in late September.  Some civil liberties groups condemned the attack. Others, including members of Congress, called for a more complete explanation of how such a targeted killing of an American civilian was consistent with the U.S. Constitution.

The Fifth Amendment provides that no one can be "deprived of life" without due process of law.  But that due process, Holder said, doesn't necessarily come from a court.

"Due process and judicial process are not one and the same, particularly when it comes to national security.  The Constitution guarantees due process, not judicial process," the attorney general said.

Holder said a U.S. citizen can legally be targeted in a foreign country if that person is "a senior leader of al-Qaida or associated forces," and is actively involved in planning to kill Americans.  Killing would be justified if the person poses an imminent threat of a violent attack against the U.S. and cannot easily be captured.

Any military operation targeting a citizen overseas must be carried out consistent with the law of war.  "The principle of humanity requires us to use weapons that will not inflict unnecessary suffering," he said.

The ACLU called Holder's explanation "a defense of the government’s chillingly broad claimed authority to conduct targeted killings of civilians, including American citizens, far from any battlefield without judicial review or public scrutiny."

"Few things are as dangerous to American liberty as the proposition that the government should be able to kill citizens anywhere in the world on the basis of legal standards and evidence that are never submitted to a court, either before or after the fact," said Hina Shamsi, director of the ACLU’s National Security Project.

"Anyone willing to trust President Obama with the power to secretly declare an American citizen an enemy of the state and order his extrajudicial killing should ask whether they would be willing to trust the next president with that dangerous power,” she said.

The ACLU is suing the Obama administration, seeking to have documents regarding the targeted killing program made public.

Holder said it makes no legal difference that a U.S. citizen is targeted away from a traditional battlefield.  "We are at war with a stateless enemy," he said.

While the U.S.-born cleric, Anwar al Awlaki, was at first believed to be merely an English speaking propagandist for the Yemen based group known as Al Qaeda in the Arabian Peninsula, U.S. officials say he gradually assumed an operational role in the terror group.

According to federal prosecutors, Umar Abdul Abdulmutallab, the underwear bomber, told FBI interrogators that al Awlaki was deeply involved in planning his attempted bombing of a Detroit bound passenger jet on Christmas day in 2009. 

Holder said Abdulmutallab told the FBI of "al Awlaki's specific instructions to wait until the airplane was over the United States before detonating the bomb."

The attorney general told the law students that the government is under no legal obligation to delay a targeted killing operation until a terrorist plotter is in the process of carrying out an actual attack.

"The Constitution does not require the president to delay action until some theoretical end stage of planning, when the precise time, place, and manner of an attack become clear," he said.

More content from msnbc.com and NBC News