Actress Allison Williams has spoken out to defend her under-fire father, insisting the U.S. broadcaster is "a truthful man" despite lying about his experiences reporting from a warzone in Iraq.

Brian Williams was suspended from his role as main anchor for NBC News for six months earlier this month (Feb15) after he was exposed for falsely claiming he was onboard a helicopter targeted by opposition gunmen during the Iraq War in 2003.

However, Girls star Allison Williams is adamant her father is not a liar and she is urging Tv bosses to put him back on air as soon as possible.

During a question-and-answer session with comedian Seth Meyers, she said, "This has been a really hard time. Obviously, (it is) toughest on my dad, who is sort of bearing the full burden of the responsibility for it, but my mom has been so strong.

"My dad has always been there for us 100 per cent of the time... so to be here for him is the least we can do... One thing this experience has not done is shake my trust and belief in him as a man.

"He's a really good man, an honest man, a truthful man. I can't wait until he's back on Tv, and I know many of you guys feel that way."

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