THE West must intervene against the Syrian government's regime to prevent "catastrophic consequences", Tony Blair has said.
The former prime minister fears both sides of the conflict will begin to use chemical weapons as an "acceptable form of warfare" if no action is taken, and urged Britain to help America arm the Syrian rebels, in an interview with The Times.
"I feel very strongly that we are in danger of a failure with catastrophic consequences," he told the newspaper.
"This is no longer a civil war between fractions within Syria. We should be taking a more interventionist line.
"You don't have to send in troops, but the international community should think about installing no-fly zones."
Last night Prime Minister David Cameron discussed the situation in Syria in an hour-long video conference with President Barack Obama, French president Francois Hollande, German chancellor Angela Merkel and Italian prime minister Enrico Letta ahead of next week's G8 summit in Lough Erne.
Mr Cameron earlier restated the Government's position that no decision had been taken to arm moderate rebels opposed to Assad, but added that he was a "brutal dictator who is using chemical weapons under our nose".
The Prime Minister backed Washington's "candid assessment" that the Syrian regime has used chemical weapons and that there is credible evidence of "multiple attacks" by Syrian President Bashar Assad's regime.
He said the UK believes the "scale of use is sanctioned and ordered by the Assad regime" but also indicated that al Qaida-linked elements in the opposition movement had also attempted to acquire chemical weapons for probable use in Syria.
Mr Obama has approved arming the Syrian rebels for the first time in response to the development, according to officials.
Speaking in the garden at 10 Downing Street yesterday, Mr Cameron said the US view was "consistent with what we have already said" about chemical weapons use.
"There is credible evidence of multiple attacks using chemical weapons in Syria, including the use of the abhorrent agent sarin," Mr Cameron said.
British experts at the Porton Down chemical warfare testing establishment have been involved in the assessment of samples taken from two sites in Syria, the Prime Minister said.
"We haven't seen any credible reporting of chemical weapons use by the Syrian opposition," he said.
"However, we assess that elements affiliated to al Qaida in the region have attempted to acquire chemical weapons for probable use in Syria."
Mr Cameron said he had to "choose my words carefully" as he revealed the information presented to him by the Joint Intelligence Committee.
The UK led calls for the European Union's arms embargo on Syria to be lifted, and Mr Cameron said evidence of chemical weapons use by Assad justified that move.
Mr Cameron said: "We have made no decision to arm the opposition, but it was right to lift the arms embargo.
"The information about chemical weapons further shows the folly of having some embargo that gives some sort of almost moral equivalence to President Assad and to the legitimate opposition. We will continue to support, train and assist and work with the opposition."
The disclosure of attempts by al Qaida-linked elements to secure chemical weapons will heighten concerns about the opposition movement and any attempts by the West to supply arms.
But Mr Cameron insisted it was right to encourage those who have a "positive, pluralistic and democratic view" of Syria's future.
He said the UK would work with allies to "do everything we can to bring this dreadful conflict to an end".
Mr Cameron told the BBC that Syria would be "up front and centre" at the G8 summit of world leaders in Northern Ireland next week.