NEW YORK (AP) - NBC News has assigned the head of its own investigative unit to look into statements that anchor Brian Williams made about his reporting in Iraq a dozen years ago, an episode that's ballooned into a full-blown credibility crisis for the network.

NBC News President Deborah Turness announced the probe in an internal memo on Friday. Williams has apologized for falsely saying on the air that he was in a helicopter hit by a rocket-propelled grenade while in Iraq in 2003, and Turness said Friday the anchor expressed his regrets to his colleagues for the impact the episode has had.

"As you would expect, we have a team dedicated to gathering the facts to help us make sense of all that has transpired," Turness wrote. "We're working on what the best next steps are."