Britain ' s government should not shy away from talking to Russia about peace in Syria, though relations with Moscow are strained, Prime Minister David Cameron said. A British inquiry on Thursday said that Russian President Vladimir Putin "probably" approved the assassination of ex-KGB agent Alexander Litvinenko in London, increasing tension between Russia and the UK. Judge Robert Owen said it was likely the Russian leader signed off the killing of the former spy in 2006 after a long-running feud. "There is no doubt that when it comes to Syria that we need all of the players, whether it is Saudi Arabia or Iran or Russia. Everyone needs to be involved," Cameron said in a wide-ranging interview with Al Jazeera on the sidelines of the Davos summit. "Obviously we have real difficulties with our relationships with Russia because of what has happened and it is right we take the action we announced yesterday, but when it comes to Syria, difficult as it is, we have to discuss these issues with them because the crisis will only be solved when all the players recognize that it is in their interest to have a settlement," he added.