NEW YORK >> 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.

A source at the network who requested anonymity because the person is not authorized to speak on personnel matters confirmed the investigation 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.

In an internal memo Friday, NBC News President Deborah Turness said Williams is apologizing to everyone at NBC for the impact the incident has had on the network.

“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.”

Richard Esposito, who has worked at the New York Daily News, New York Newsday and ABC and is now at NBC, is leading the investigation. There was no immediate word on whether Williams would anchor NBC’s “Nightly News” on Friday.

Williams’ story about his wartime reporting experience made him a subject of mockery, including a New York Post front cover that depicted him with a long Pinocchio’s nose, over the headline “A Nose for News.”

He’s the leading man at the network’s news division, whose nightly newscast has topped its rivals in ratings for the better part of a decade. As a frequent talk show guest and one-time “Saturday Night Live” host, his celebrity transcended the news division.

He apologized on the air Wednesday for telling his story about the supposed grenade attack as recently as last Friday on “Nightly News.” He admitted that his helicopter was not hit by a grenade after war veterans had come forward to question the account, some even disputing whether Williams’ helicopter was in a group that came under direct attack.

NBC News needs to look at not only Williams’ story, which has changed in details as he’s talked about it over the years, but whether anybody else at the network knew that he was spreading a falsehood and did anything about it, said Kelly McBride, an expert on ethics for the journalism think tank the Poynter Institute.

“He is the front man of ‘Nightly News’ and is seen as the primary arbiter of the facts,” McBride said. “For him to get something wrong on something he was involved in casts doubt on his ability to get any facts right.”

NBC News must also weigh his importance to the news division and the work he has done since taking over as top anchor from Tom Brokaw in 2004, she said. Brokaw, for his part, on Friday denied a published report that he had suggested Williams be dismissed.

“Brian’s future will be decided by him and the executives of NBC News,” Brokaw said.

That would be Deborah Turness and her immediate supervisor, Pat Fili-Krushel, who had seen “Nightly News” as a bright spot for the network as they tried to correct ratings problems at the “Today” show and “Meet the Press.” NBC’s corporate parents at Comcast would likely weigh in as well.

Meanwhile Friday, CNN said it was stepping back from its own report Thursday, quoting Rich Krell, a veteran who claimed to pilot Williams’ helicopter in Iraq. Krell had said Thursday that the helicopter had taken small arms fire — if not a grenade attack — but said Friday that he was questioning his own recollections after being contradicted by other veterans.