WMD fiasco under Tony Blair has hit the West's fight against Assad, says David Cameron Blair's false alarm over Iraq has stopped leaders tackling Assad says PM Britain and the US have accused Assad of using chemical weapon sarin Obama warned the chemical weapons should be 'a red line' for intervention By David Williams and Tim Shipman David Cameron yesterday warned that the furore over false intelligence about Iraq's weapons of mass destruction was stopping Western leaders getting tough with Syria. After accusing Syria's Bashar al-Assad of war crimes by using the chemical weapon sarin, he admitted the WMD blunders made by Tony Blair's government offered an excuse for leaders to do nothing. Mr Cameron said: "I do worry about that. I think the Iraq lesson must be about how we marshal and use information and intelligence and I think that lesson has been learned. Crisis: As the Syrian civil war rages on, this week the Obama administration announced that as well as conventional weapons, President Assad has used chemical weapons on civilians Recent interview: President Bashar Assad accused the West on Wednesday of backing al-Qaeda in his country's civil war this week But I think it is very important for politicians and leaders of this generation to look at what is happening in Syria and ask ourselves what more we can do. Earlier Mr Cameron ramped up the rhetoric against Assad over the alleged use of sarin. "It is extremely serious, this is a war crime, and we should take it very seriously," he said. He echoed Barack Obama by warning "this should form for the international community a red line for us to do more." That is code for military intervention by the West. His statements make British and US air strikes far more likely and officials admit that imposing a "no-fly zone" over Syria is definitely "on the table" for top-level discussion. However, Mr Cameron ruled out sending British troops into Syria saying: "Do I think putting troops on the ground in Syria is the right thing to do, as we did in Iraq and Afghanistan? No, I don't. Should we be working with our allies, the French, Americans, others in the Gulf to support the responsible part of the opposition, do everything we can? To train them, to work with them so they can support their people, to put pressure on the regime? Yes, we should. Criticism: David Cameron, right, openly said that the misuse of intelligence under Tony Blair, left, was discouraging leaders from acting over the Syrian civil war Mr Cameron is expected to lead a National Security Council meeting and talk to Mr Obama next week. National Security Adviser Sir Kim Darroch held video conferences this week with his American opposite number Tom Donilon. Meanwhile, Government scientists at the Defence Science and Technology Laboratory at Porton Down, Wiltshire, have analysed samples smuggled out of Syria and confirmed they are sarin. The samples probably include ones from the Syrian government's attack on April 13 near the city of Aleppo. MI6 officers are also working with the CIA to gather intelligence on the exact circumstances in which chemical weapons were used. Dilemma: President Barack Obama faces a hard decision over the ongoing situation in Syria as he said that use of chemical weapons by Assad was the 'red line' British diplomats want to present concrete evidence to the UN Security Council that chemical weapons were used. They need to secure support from Russia for international intervention. Moscow has so far blocked UN action. Asked if air strikes and a no-fly zone are under consideration, a senior Government source said: "Nothing is off the table. These are issues that we will be exploring with our allies. The priority is to obtain the full facts. The Russians have previously taken the same view as us on the use of chemical weapons so there may be an opportunity to get some movement at the UN. But before we make that case we need the full facts. It is feared that Syria's large arsenal of chemical weapons, approximately 1,000 tons, stored in 50 towns and cities, could fall into the hands of Al Qaeda. US special forces are understood to have devised plans to seize control of the arsenal, but sources here denied Britain will help them. Despite the mounting evidence Syria continues to deny using chemical weapons. Syrian official Sharif Shehadeh called the US claims "lies" and likened them to false accusations that Iraq possessed weapons of mass destruction ahead of the US-led invasion.