Some of the blood samples used by France were smuggled out of Syria by Le Monde journalists and reportedly supplied by local doctors. There were no details on how France obtained other samples used. In only one case has Fabius claimed that the use of sarin is directly attributed to government forces, saying there was "no doubt that it was the regime and its accomplices."
A UK spokesman was more equivocal, stating that there could be no "100 percent certainty" that the Assad regime had used chemical weapons. The FCO would not even confirm where or when its samples were collected. Mark Lyall Grant, Britain's ambassador to the United Nations, stated only that they revealed evidence suggesting use of a number of different chemical agents, "sometimes including sarin, sometimes not."
Ake Sellstrom, who heads the UN investigation, issued a statement cautioning that "the validity of the information is not ensured in the absence of convincing evidence of the chain of custody of the data collected."
Ultimately, what happens next will not be decided in Paris or London, but in Washington.
President Barack Obama has warned that use of chemical weapons crosses a "red line," but there are divisions over how far and how fast to proceed against Syria.
After discussing France's and Britain's claims Tuesday evening at a meeting of NATO defence ministers in Brussels, Defence Secretary Chuck Hagel told reporters that he had not seen the evidence and that NATO's role continues to be to help protect alliance members such as Turkey. "[B]eyond that we didn't get into any additional war plans regarding Syria," he said.
There is no popular support in the US for war against Syria, and a great deal to lose if things go wrong for the ruling class. That is why, to date, the Obama administration has preferred to proceed through local intermediaries -- the FSA and its regional backers, Turkey and Gulf States such as Saudi Arabia and Qatar. It wants to eliminate Assad as an ally of Iran, without unduly provoking Russia, and is seeking to cook up a replacement regime that is acceptable to Moscow.
There is in addition mounting concern that the conflict is rapidly spreading out of control, dragging in neighbouring Lebanon and Iraq and even Israel. There are divisions over how to respond, with Republicans such as Senator John McCain and former Secretary of State Condoleezza Rice lobbying hard for Obama to make good on his "red line" threat.
Russian President Vladimir Putin said on Tuesday that Moscow had so far refrained from supplying the powerful S-300 surface-to-air missile systems to Damascus he had earlier said would be a "stabilising factor" and would deter foreign intervention in Syria.
After talks Tuesday with European Union leaders in Yekaterinburg, Putin said the contract signed several years ago had not yet "been realised" because, "We do not want to upset the balance in the region."
He warned, however, that, "Any attempts to influence the situation by force through direct military action is doomed to fail and would unavoidably bring about large humanitarian casualties."