NEW YORK - NBC News has assigned the head of its investigative unit to look into statements 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 in Iraq in 2003, and Turness said Friday that he expressed his regrets to his colleagues for the effects 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."

Richard Esposito, who has worked at the New York Daily News, Newsday, and ABC and is now at NBC, is leading the investigation.

Williams, who has been widely chastised, anchored Nightly News from New York on Friday, making no mention of the criticisms of his work.

Questions also were raised about statements Williams made on coverage of Hurricane Katrina, which was one of his proudest moments at NBC. In a 2006 interview with former Disney CEO Michael Eisner, Williams twice referenced seeing a body float down a street in New Orleans.

"When you look out of your hotel room window in the French Quarter and watch a man float by face down, when you see bodies that you last saw in Banda Aceh, Indonesia, and swore to yourself that you would never see in your country," Williams said.

Several minutes later, Williams again talked about seeing the body as he discussed how it felt to cover the storm.

"I felt something get dislodged that changes the usual arm's length relationship between me and the stories I cover," he said. "These are Americans. These are my brothers and sisters. And one of them was floating by."

The remarks drew suspicion because during Katrina there was relatively little flooding in New Orleans' French Quarter.

Williams was staying at the Ritz-Carlton hotel in New Orleans, according to an NBC source who was not authorized to speak on personnel matters and requested anonymity.

Police Capt. James Scott, who was a commander in the downtown area, said he saw a body floating along the edge of the French Quarter on a street about four blocks from the Ritz-Carlton, which was surrounded by up to 3 feet of water.

Alex Brandon, a Washington-based photographer for the Associated Press, said there was enough water to launch a flat-bottomed boat from in front of the Ritz. He said he photographed a body floating on another street a few blocks from the Ritz.