UK: We Have New Evidence Poison Gas Used in Syria U.K. scientists have found new evidence that poison gas was used last month outside the Syrian capital of Damascus, British Prime Minister David Cameron said Thursday In an interview with BBC television on Thursday, Cameron said that the evidence being examined by experts at England's Porton Down Laboratory "further shows the use of chemical weapons in that Damascus suburb." The BBC's account of the interview did not make clear whether the British tests had determined who was responsible for the chemical strike - a critical question facing world leaders as they gather in St. Petersburg to debate an international response to the August 21 attacks. Some Western leaders, including President Barack Obama and his chief diplomat, John Kerry, have said there's no doubt that the gassing was the work of the Syrian government, headed by President Bashar Assad. But U.S. officials have told The Associated Press there are still holes in the case against Assad, and other leaders - including Cameron - have acknowledged lingering uncertainty over who exactly was behind the strike. Nevertheless, the BBC quoted Cameron as saying that evidence of the Assad government's culpability was "growing all the time." A spokesman for Cameron's office said the evidence referred to by the prime minister in his interview consisted of clothing from one of the reported victims and some soil taken from the area. Both samples tested positive for the deadly nerve gas sarin, he said, speaking on condition of anonymity because he was not authorized to be quoted by name. Kerry said on Sunday that Washington has evidence of sarin gas use. Cameron declined to comment on how or when the evidence made its way to Britain, citing security concerns. Porton Down, where the samples are being examined, has a nearly 100-year-old of chemical weapons research. The lab, roughly 85 miles (135 kilometers) west of London, was established in World War I as the center of Britain's chemical warfare program, and tests on a variety of chemical and biological agents continued there in World War II and throughout the Cold War.