According to a report in The Times of London, British scientists have found evidence for the first time that "some kind of chemical weapon" was used at least once in Syria. According to the U.K. daily, a soil sample was smuggled out of the country in a British operation.

The Times article cited unnamed defense sources as having said that scientists had established "conclusive proof" of the weapon's use at a Ministry of Defense research establishment in the U.K.

The tests were conducted at the Ministry of Defense research facility in Porton Down, Wiltshire. According to the Times report, the tests showed that the traces of chemicals were from a weapon rather than riot-control gas that is sometimes employed by Syrian security forces at protests.

A source told the Times: "There have been some reports that it was just a strong riot-control agent but that is not the case - it's something else although it can't definitively be said to be sarin nerve agent."

The Syrian government and the country's rebel groups have accused each other of using chemical weapons in the past, though no definite evidence has been found so far.

Intelligence officials in the West concluded last week that forces loyal to Syrian President Bashar Assad used chemical weapons in their war against rebels. The information relates to two incidents in the Damascus area on March 19 – one near Halab and one in the area of Damascus. However, various intelligence agencies, first and foremost the Americans, have not concluded whether the material used was a toxic chemical or a material that paralyzes only and does not kill.

At the end of March there were reports that western intelligence agencies believed that it was actually the rebels who had used chemical weapons, having succeeded, by an undetermined method, to fire chlorine gas at a Syrian army checkpoint at Khan al-Assal, a village near Halab. According to these reports, 26 people were killed in that attack and dozens were injured.

If there is conclusive proof that chemical weapons have been used, this may lead to an acceleration of Western involvement in the conflict. The United States has warned that use of chemical weapons would be a "red line."

“We will not tolerate the use of chemical weapons against the Syrian people,” U.S. President Barack Obama said in his address last month at the Jerusalem International Convention Center, two days after the use of chemical weapons was first reported. “The world is watching, and we will hold you accountable.”