Since the deadly attacks which killed more than a thousand civilians in Syria last month, there’s been debate about whether chemical weapons were used and if so, who used them. Now the U.K. says there’s new evidence that chemical weapons were indeed used.

Syria

U.K. presents evidence of sarin

U.K. Prime Minister David Cameron told the BBC today that laboratories in his country have been examining samples taken from the attacks at Damascus. The Independent reports that Cameron said those samples tested positive for sarin, a deadly nerve agent which can kill an adult in less than two minutes with a drop the size of a pin prick. The samples were tested by the U.K.’s secrete Porton Down laboratories and reportedly came from soil in the area where the attack occurred and clothing worn by one of the victims.

Cameron said the samples were obtained separately from those obtained by the U.S. and France, which already tested positive for sarin.

G20 summit continues in Russia

Meanwhile leaders of some of the world’s biggest nations are meeting at the G20 summit today in St. Petersburg, Russia. Cameron said the U.K. would lead the argument for getting humanitarian aid to Syria and bring plans for a peace process. He said the nation would also continue to lead the argument for a strong response to the use of chemical weapons.

U.S. President Barack Obama has been holding informal talks in an attempt to drum up support for a strike against Syrian President Bashar al-Assad. His regime is suspected of having used the chemical weapons on a few occasions, including the large attack which killed more than 1,400 civilians, including many children, on Aug. 21. The Assad regime has denied using chemical weapons and has said they would not change their position even if World War 3 erupts.

Even though U.K. lawmakers voted against involvement in the conflict in Syria, Cameron urged Obama not to hold back from striking Syria because that could signal to other global dictators that the use of chemical weapons will be tolerated.

Russian President Vladimir Putin, who is hosting the G20 summit, called a strike against Syria without the approval of the United Nations “an aggression.” Pope Francis is also warning against unnecessary military action, saying that an attack on Syria would not solve the problem.