Earlier this week, Brian Williams admitted that his story that he was under fire during the invasion of Iraq more than a decade ago was false. Now, the NBC News veteran is facing heavy scrutiny for the blunder.

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"I made a mistake in recalling the events 12 years ago," Williams said on Wednesday's NBC Nightly News broadcast. "I want to apologize. I said I was travelling in an aircraft hit by RPG [rocket-propelled grenade] fire. I was actually instead in a following aircraft."

Williams first reported the incident in 2003, and at the time he did not claim to be in the aircraft that was struck by ground fire. But in a 2013 appearance on Late Show, he gave a more dramatic retelling to David Letterman.

"Two of our four helicopters were hit by ground fire, including the one I was in -- no kidding!" Williams told the talk show host nearly two years ago. "RPG and AK 47 ... We got hit and I just came away with more respect for these men and women."

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Williams reiterated the claims as recently as last week, during a tribute piece on NBC Nightly News. A Facebook post Williams wrote attracted responses from some of the veterans who were on the mission, calling the newsman "a fake" and "a liar."

"I think his credibility is hurt but not ruined," Brian Stelter, CNN senior media correspondent, told ET. "I think NBC may just want to push through this and hope people give him the benefit the doubt."