Britain has “limited but persuasive” evidence of the use of chemical weapons in Syria, including sarin gas, the Foreign Office said today, following similar comments by US officials.

“We have limited but persuasive information from various sources showing chemical weapon use in Syria, including sarin,” a Foreign Office spokeswoman said.

“This is extremely concerning. Use of chemical weapons is a war crime,” she added.

“We have briefed our allies, partners and the UN on this information and we are working actively to get more and better information.”

Reports earlier this month said British military scientists had studied a soil sample brought back from an area close to Damascus and found it tested positive for chemical weapons, although the government has not confirmed that.

The British announcement came shortly after the White House said that Syria had likely used chemical weapons against rebel forces on a “small scale”, but emphasised US spy agencies were still not 100 percent sure.

Washington has repeatedly said that chemical weapons use by Syrian President Bashar al-Assad’s regime would cross a “red line”, triggering possible military action.

Britain said Syria must allow in international observers.

“Assad must cooperate with the international community and prove that his regime has not committed this horrific crime, allowing unrestricted access for the UN and OPCW (Organisation for the Prohibition of Chemical Weapons) to investigate on the ground in Syria,” the Foreign Office spokeswoman said.

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