UK Prime Minister David Cameron has used his participation in the G-20 summit in St. Petersburg, Russia, to present new evidence of the use of chemical weapons in the Syrian conflict.

He said British laboratory tests have confirmed that the lethal sarin nerve gas was used in the chemical attack in the suburb of Damascus back in August.

The Guardian writes Friday that positive tests for sarin were completed this week and made on clothes and soil taken from the site of the attack in Ghouta, eastern Damascus on August 21. The tests were carried out in the past seven days by British scientists at the Porton Down facility.

"All the testing that's been done, including the testing we are doing at our Porton Down laboratories, all adds to the picture. But I don't think anyone is seriously denying that a chemical weapons attack took place. I think the Russians accept that. Even the Iranians accept that," Cameron said.

The samples brought to the UK from the Syrian borders are different to the hair and blood samples tested in the US. Details of those test results were released by the US secretary of state, John Kerry, four days ago.

British sources did not give further details of the precise content of the UK tests, but said they were confident the samples had not been tampered with during their passage to the Syrian border, and then to the UK.

German intelligence this week claimed to have intercept evidence revealing the Syrian military had been behind the attacks.

The results of the UN onsite inspection are yet to be revealed.

Cameron presented the latest evidence in a fresh attempt to persuade Russian President, Vladimir Putin, to do more to force the Syrian president, Bashar al-Assad, to the negotiating table.

After refusing to put the issue of Syria on to the agenda, Putin relented on Thursday and said the crisis would be discussed over dinner at the summit. Discussions during the afternoon had concentrated on economic matters.

Cameron also used the occasion to deny he had been sidelined by the Commons vote last week to reject UK involvement in military action in Syria.

"Some MPs had become isolationist. For some people there will never be enough evidence and for some in the debate in the House of Commons it wasn't about evidence, it wasn't about chemical weapons, it was about how they felt let down over Iraq and a deep concern – which I completely understand – about not wanting to get further involved in the difficulties in Syria," The Guardian quotes him as saying.

Meanwhile, with Russia, al-Assad's strongest ally, expected to use its veto power to block any military action against Syria, US ambassador to the United Nations Samantha Power accused the country of holding the UN Security Council "hostage" over the crisis.

"Russia continues to hold the Council hostage and shirks its international responsibilities," she said.

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