Russian President Vladimir Putin and British premier David Cameron failed to hide their differences on the Syrian crisis on Thursday before the two leaders watched the Olympic judo together. On his first visit to Britain for seven years, Putin pledged to work with Cameron to bring Syria\'s bloody 17-month conflict to an end. But after 45 minutes of talks at his Downing Street residence, Cameron acknowledged there was still a gulf between the two countries\' stances on President Bashar al-Assad\'s regime and the spiralling violence in Syria. \"There have been some differences in the positions that we\'ve taken over the Syrian conflict,\" Cameron told reporters. \"We both want to see an end to that conflict and a stable Syria, and will continue to discuss with our foreign ministers how we can take this forward,\" he added. Britain has been strongly critical of Russia\'s action to block UN action on the Syrian conflict, which human rights monitors say has killed 20,000 people. Russia and China have jointly blocked three UN Security Council resolutions that would have imposed sanctions on Assad\'s government for its crackdown on the opposition, and have refused to join international calls for his departure. The talks between Putin and Cameron took place shortly before Kofi Annan announced he was quitting as UN-Arab League envoy for Syria after battling in vain to persuade Assad to accept a peace plan. Moscow\'s UN envoy said that Russia regretted the former UN chief and Nobel peace laureate\'s decision to step down. \"We understand that that\'s his decision; we regret that he chose to do so,\" Ambassador Vitaly Churkin told reporters at UN headquarters, insisting that Russia had always supported the envoy \"very strongly.\" Putin made no direct reference following the talks with Cameron to Russia\'s continuing support for Assad, but said there were some areas where Moscow and London \"see eye-to-eye\". \"We agreed to continue working to find a viable solution,\" he said. The two leaders headed in separate cars after the talks to the ExCeL Centre in east London, a giant conference centre where the Olympic judo competition is being held. Putin is a black belt in the martial art and has often been filmed in Russia training with judokas as part of his image as a sportsman and lover of rugged pursuits. The leaders sat together at the arena and talked animatedly through a translator as they watched Russia\'s Tagir Khaibulaev take the gold in the men\'s under-100kg category. Putin threw his arms in the air and hugged Russian fans as he went to greet the winning judoka. Cameron\'s presence, however, brought less luck to Britain\'s Gemma Gibbons, who lost out to US judoka Kayla Harrison in the battle for the under-78kg women\'s title and had to settle for silver. Queen Elizabeth II\'s husband Prince Philip also paid a brief visit to the judo. It was Putin\'s first visit to Britain since the G8 summit at Gleneagles in 2005, a year before British-Russian relations plunged into deep freeze after Kremlin critic Alexander Litvinenko was killed by radiation poisoning in London. Cameron visited Moscow last year in a bid to break the ice and he and Putin\'s predecessor Dmitry Medvedev -- now Russia\'s prime minister -- vowed to heal relations. The British premier also met with Putin on that occasion in the first high-level contact between the Russian and any British minister or diplomat since 2007, but the two countries remain far apart on the Litvinenko case. Russia\'s refusal to extradite Andrei Lugovoi, the chief suspect in the murder who later became a lawmaker, led to a sharp deterioration in ties. Lugovoi, who is accused of lacing Litvinenko\'s tea with polonium, denies any involvement.