More evidence for more action

British Prime Minister David Cameron told the BBC on Friday that there was limited but growing evidence of chemical weapons' use by forces loyal to President Bashar al-Assad's regime.

"It is very disturbing what we are seeing," Cameron said. "It's limited evidence but there's growing evidence, that we have seen too, of the use of chemical weapons, probably by the regime."

His comments came one day after the US reported that Syria had likely used chemical weapons against rebel forces, but emphasized that spy agencies were still not 100 percent sure of the assessment. The chemical used is believed to be sarin, a highly toxic nerve agent.

At the start of the inquiry, President Barack Obama said that any evidence that the regime has used chemical weapons would be a "game changer."

"This is extremely serious, and I think what President Obama said was absolutely right - that this should form for the international community a red line for us to do more," Cameron said.

Cameron stopped short of calling for military action. "I don't want to see that and I don't think that is likely to happen, but I think we can step up the pressure on the regime, work with our partners, work with the opposition in order to bring about the right outcome."

Calling the alleged actions “appalling” he said more evidence needs to be gathered.

"In my view what we need to do ... is shape that opposition, work with them, train them, mentor them, help them so we put the pressure on the regime and so we can bring this to an end," he said.

Britain's Foreign Office confirmed Thursday it also had "limited but persuasive" evidence of the use of chemical agents in the conflict, which has left more than 70,000 dead since March 2011, according to the United Nations.

Government forces and rebels have accused each other of using chemical weapons. The United Nations has set up a mission to investigate the allegations. However, Syria has refused to allow the UN team into the country.

EU waiting for definitive evidence

Meanwhile, the European Union anounced that it was waiting for more definitive evidence on whether the regime had used chemical weapons.

"We are still monitoring this along with our international partners to see what has really happened because it doesn't seem entirely clear at this point in time," said Michael Mann, a spokesman for EU foreign policy chief Catherine Ashton.

"The line we have is very, very simple: that any use of chemical weapons in any circumstances is, of course, completely unacceptable," he said.

hc/jm (AFP, dpa)