Russian President, Vladimir Putin

Black-belted Vladimir Putin locked horns on Thursday with British leader David Cameron over Syria and a crackdown on Kremlin opponents before heading for an afternoon of judo diplomacy at the Olympic Games.

Prime Minister Cameron tried to push the former KGB spy to take a tougher line on Syria, Russia's firmest foothold in the Middle East, and stop blocking Western-backed resolutions aimed at stepping up pressure on President Bashar al-Assad.

But after 45 minutes of talks in Downing Street, for which Putin put in an unusually punctual appearance, Cameron and Putin said Russia and Britain still differed over Syria, reports Reuters.

"I look forward to taking the president to the judo but note that we will be spectators, not participants," Cameron told reporters, then the two men travelled to the Olympics.

Cameron raised the fate of female punk band, Pussy Riot, whose members are on trial in Moscow for anti-Putin lyrics, with the Russian president as part of wider talks on human rights.

In a stark illustration of the still frosty ties between Britain and Russia, Putin used his stretched, Russian-number-plated black Mercedes limousine while Cameron used his armored grey Jaguar to leave Downing Street.

The two leaders entered the Olympic judo arena together just seconds after British fighter Gemma Gibbons pulled off a shock win over the world champion to get to the final of one of the women's competitions.

A one-time judo champion in his native city of St Petersburg, Putin talked animatedly with Cameron through a translator and appeared to be explaining judo to the prime minister, who in March watched basketball with U.S. President Barack Obama in Ohio.

For the 59-year-old Kremlin leader, who revels in his hard-man image, the sight of judokas body-slamming each other on the Olympic mats offered a powerful backdrop to his talks with Cameron.

Putin's body language was closely watched for signs about the progress of the talks on his first visit to London since 2003. His last visit to Britain was to attend the Group of Eight summit in 2005 at Gleneagles in Scotland.

In previous foreign trips, Putin has even showed off his judo skills on the mats and London Mayor Boris Johnson, who is known for his own publicity stunts, said he hoped Putin would strip off to take part.

"Oh, I hope he will take part. What is he, a dab (hand), I think that's what we want to see, stripped to the waist. We want the politicians Olympics, that's what we want," Johnson said.

But Putin, tanned and dressed in a red necktie and dark suit, appeared to be focused on the judo bout in which Russia's Tagir Khaibulaev won, sealing his place in the 100-kg men's final against Olympic champion Tuvshinbayar Naidan of Mongolia.

Putin showed little emotion and just clapped while Russians -- one even dressed in a white fur hat -- waved the Russian red, blue and white flag embossed with the two headed Russian eagle.