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US actor Will Ferrell has been awarded his country's top comedy awards, the Mark Twain Prize for American Humor.

Ferrell, who impersonated George W Bush on sketch show Saturday Night Live, was given the award at the Kennedy Center for Performing Arts in Washington DC.

The screen star joked he had turned down the prize 13 times before.

Conan O'Brien, Jack Black and Ben Stiller were among stars who paid tribute to Ferrell at a ceremony that will be televised on PBS on 31 October.

When Ferrell was awarded the bronze bust of Twain, he dropped it on the floor and tried to pick up the pieces.

The Anchorman and Zoolander star, who co-founded comedy website Funny Or Die, said he had decided to accept the award so that he could be watched on PBS "by hundreds of people across the country".

Jack Black opened the show with a musical routine, changing the words of Queen's We Will Rock You to: "Will will, Will will, rock you."

Black also paid tribute to Ferrell as "crazy funny - he makes you laugh so hard you cry and pee simultaneously".

O'Brien, meanwhile, joked about his own short stint as host of NBC talk show 2009 and 2010.

He thanked Ferrell for being his first and last guest on the show.

"It's a rare friend who's going to stick with you for five-and-a-half months," he said.

Video clips of some of Ferrell's Saturday Night Live appearances were also shown.

Ferrell appeared on the show from 1995 to 2002 and impersonated Neil Diamond, Saddam Hussein and Fidel Castro among others.

His comedy drama Everything Must Go, about an alcoholic who holds a yard sale after losing his job, was released in the UK on 14 October.

Previous winners of the Mark Twain Prize include Tina Fey, Billy Cosby, Steve Martin, Whoopi Goldberg and Richard Pryor.