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Brian Williams backs out of Letterman appearance

NEW YORK -- Embattled NBC News anchor Brian Williams is backing out of scheduled appearance on David Letterman's "Late Show" on Thursday.

Brian Williams to take temporary leave from NBC newscast

That news from NBC came Sunday, a day after Williams said he was stepping away from NBC's "Nightly News" as the network looks into the anchor's admission that he had told a false story about being on helicopter hit by a grenade while reporting on the Iraq war.

Weekend anchor Lester Holt is filling in for Williams on the "Nightly News" for at least the next several days.

Williams anchored "Nightly News" Friday but did not mention the controversy which has generated dozens of negative headlines. He apologized during the program earlier this week for falsely saying on the air that he was in a helicopter hit by a rocket-propelled grenade while in Iraq in 2003.

Williams also recounted the story when he appeared on "Late Show with David Letterman" in 2013:

Richard Esposito, a former editor at the New York Daily News now at NBC, will head the company's investigation, according to the Associated Press. The incident has ballooned into a full-blown crisis for NBC and Williams, whose "Nightly News" is the top-rated evening news program.

Williams is now facing new scrutiny for some comments he made about his coverage of Hurricane Katrina in New Orleans. In a 2006 interview with former Disney CEO Michael Eisner, Williams recounted seeing a corpse float by from his hotel in the French Quarter.