Discuss as:

Obama to appoint Comey to head FBI: Sources

Alex Wong / Getty Images file

Former U.S. Deputy Attorney General James Comey testifies during a hearing before the House Commercial and Administrative Law Subcommittee of the Judiciary Committee May 3, 2007 on Capitol Hill in Washington, DC.

President Barack Obama intends to nominate former deputy attorney general James Comey to succeed Robert Mueller as FBI Director, sources familiar with the decision told NBC News on Wednesday.

Comey, a Republican who served under President George W. Bush, would take over after Mueller steps down in September.

Mueller, who has previously made public his long-term plans to step down in the coming months, has spent 12 years as head of the FBI. He has recently faced some scrutiny over the agency's failure to more thoroughly investigate Boston bombing suspects Tamerlan and Dzhokhar Tsarnaev after being alerted by foreign agencies.

Mueller took over the FBI just one week before the Sept. 11, 2001 attacks.