"The end of an era?"

Crowds boo Vladimir Putin

Opponents of Vladimir Putin hailed an unprecedented show of public protest after the Russian prime minister was loudly booed by the crowd at a no-holds-barred fight night.

Mr Putin faced whistles and boos on live television as he congratulated a Russian champion in the fighting – a sport in which the tough guy premier has always shown great interest – after his victory over an American.

He climbed into the ring on Sunday evening after the blood-spattered bout between Russian heavyweight champion Fedor Emelianenko and Jeff Monson, but the start of his speech was drowned out by boos and whistles.

Viewers uploaded the television footage to YouTube, where it has gone viral.

Mr Putin hugs Emelianenko and launches into a speech, but appears to pause as the crowd greets his opening line with whistles and low-pitched booing. It only breaks into cheers as he praises Emelianenko as a "real Russian hero".

The speech was a rare public relations failure for the premier, whose television appearances are usually tightly stage-managed, although opinions varied on Monday as to whether the boos were specifically directed at Putin.

Blogger Alexei Navalny, famed for exposing corruption, posted the video on his site and wrote that it was "the end of an era".

"Up till now there have never been any displays of dislike of Putin at any public event," wrote the Gazeta.ru news website.

But the director of the Olimpiisky stadium which hosted the fight, Mikhail Moskalyov, told Lenta.ru news website that the audience was reacting as the American fighter left the ring.

Mr Putin's speech at the match would appear to fit in with his strongman image and passion for judo, in which he has a black belt. But he rarely speaks impromptu to untried audiences.

Kremlin official Kristina Potupchik, spokeswoman for Kremlin youth group Nashi, also dismissed suggestions that people had jeered. She insisted that the shouts were instead because people in the audience couldn't get to the toilets.

"People, have you gone completely mad? I was at Olimpisky tonight, people were screaming and whistling from happiness," she wrote.

"Some of the 22,000, their bladders filled with beer, started to protest against their inability to empty them. Yes, that happens. You should go to the toilet beforehand, gentlemen."

Emelianenko competes in the brutal Russian sport called mixed martial arts, which allows blows with legs and hands. It is also known in the country, somewhat appropriately, as "fight without rules."

Monson finished the match limping and covered in blood after a blow to his face. The sport, a mixture of boxing, wrestling and kick boxing, is known in the West largely as ultimate fighting or no-holds-barred fighting.