Washington. US Secretary of State John Kerry has warned that not responding to the alleged use of chemical weapons by Syrian forces would be riskier than taking action.He was speaking in London before returning to the US to urge Congress to back launching military strikes.Russia has appealed to Washington to focus instead on peace talks.Syria’s President Bashar al-Assad has said if the US does attack militarily, it should "expect every action”.The US accuses Mr Assad’s forces of killing 1,429 people in a poison-gas attack on 21 August on the outskirts of the capital, Damascus. Wrapping up a tour of European capitals, Mr Kerry said that if there was to be no response to the attack, then Damascus would think it could intimidate anybody."I don’t believe that we should shy from this moment: the risk of not acting is greater than the risk of acting,” he said.Mr Kerry was speaking as details emerged of a US television interview given by President Assad in which he warned of some kind of retaliation if a strike was made,"You should expect everything, not necessarily from the government,” Mr Assad told CBS TV in an apparent reference to Syria’s allies, Iran and the militant Hezbollah movement in Lebanon."There has been no evidence that I used chemical weapons against my own people,” he added. The Syrian leader would neither confirm nor deny his government kept chemical weapons, but said that if they existed, they were "in centralised control”. Speaking in Moscow on Monday, Syrian Foreign Minister Walid Muallem accused the US of using the issue of chemical weapons as a "pretext” to launch a war.He addressed reporters alongside Russian Foreign Minister Sergei Lavrov who insisted there was no alternative to a peaceful solution to the crisis, adding that Mr Muallem had confirmed Damascus was prepared to take part in a Geneva conference."We appeal to our American colleagues to concentrate on this and not for preparing for a war scenario”, Mr Lavrov said. But the secretary of state appeared to cast doubt on this approach in his remarks minutes later in London: "If one party believes that he can rub out countless numbers of his own citizens with impunity using chemical weapons... he will never come to a negotiating table.”Mr Kerry has been lobbying hard for military action against Mr Assad during talks with EU and Arab foreign ministers before his return to Washington.Mr Assad’s government blames the attack on rebels fighting to overthrow him in the country’s two-and-a-half-year civil war, which has claimed some 100,000 lives, according to UN estimates.UK Foreign Secretary William Hague cautioned against believing anything from President Assad’s interview."We mustn’t fall into the trap of attaching too much credibility to the words of a leader - President Assad - who has presided over so many war crimes and crimes against humanity,” Mr Hague said.Politicians will be back at work in Washington on Monday after their summer recess to start discussing President Barack Obama’s resolution to launch a "limited, narrow” strike.