LONDON (AFP) - Prime Minister David Cameron said on Thursday that Britain had further evidence of the use of chemical weapons in Syria, which a British source said confirmed the use of sarin.

"We have just been looking at some samples taken from Damascus in the Porton Down laboratory in Britain which further shows the use of chemical weapons in that Damascus suburb," Mr Cameron told BBC TV from the G20 summit in St Petersburg.

A British source said that a soil and cloth sample taken from the site of the alleged chemical attack in the Syrian capital "has tested positive for sarin".

The source said the results were separate to those obtained by the United States, which has said it has proof of the use of sarin in last month's attack.

Last week British lawmakers voted against taking military action against President Bashar al-Assad's regime, which has been blamed for the attack.

The regime claims the rebels were responsible.