France and Britain have both confirmed for the first time that chemical arms were used in Syria and Paris says a line has been crossed. So what next in a conflict that has cost over 94,000 lives?
Not much, experts predict, amid resistance from Syria allies Russia and China and ahead of a proposed peace conference, coupled with painful memories of the Iraq war, which was justified by supposed evidence of weapons of mass destruction that never materialised.
Nadim Shehadi, associate fellow at the Chatham House international affairs think-tank's Middle East and North Africa programme, said the confirmation was only significant "if it leads to some action or intervention."
"And I think if it does, it's the worst excuse to use. Because immediately it will remind people of the Iraq excuse. There is enough reason for intervention with the massacres that the regime is doing," he said.
"The red line should have been the regime killing its people. We created an artificial red line to say the regime can kill its people as long as it doesn't use any chemical weapons."
French Foreign Minister Laurent Fabius on Tuesday announced for the first time that Paris had proof the deadly nerve agent sarin gas had been used in Syria several times.
He said in a televised interview that in at least one case, there was "no doubt that it was the regime and its accomplices", adding that "a line has been indisputably breached."
Soon after Fabius's comments, London followed suit, saying it had its own evidence of the use of the odourless, paralysing gas. But the United States remained cautious and said more proof was needed.
"There is no willingness to intervene," said Obaida al Moufti, spokesman for the Union of Syrian Medical Relief Organizations, which is backed by France and operates covertly in Syria.
Signup to our newsletter and follow us on Facebook and Twitter!
The organisation estimates some 70 people have been killed by chemical weapons in Syria -- small fry compared to the tens of thousands of others who have died since March 2011 when the conflict began.
Paris and London have called for "immediate and unconditional access" to Syria of United Nations investigators -- access which has so far been refused.
And a French diplomatic source said there is talk of going to the UN Security Council, where two of the permanent members -- Russia and China -- have blocked resolutions condemning Assad three times already.
However France says Russia is on the same wavelength where chemical weapons are concerned and believes that a "unanimous condemnation would already be very strong", said the diplomat.
The sarin gas confirmation comes as global powers attempt to organise a peace conference on Syria that would bring together members of the regime and opposition in Geneva.
The regime has agreed in principle to participate, but Syria's main opposition has refused to attend as long as fighters from Iran and the Islamist-militia Hezbollah are fighting in Syria alongside Assad's forces.
"The international community is expecting after all this that the opposition will go to Geneva to accept to talk to Assad. Totally unreal," said Shehadi.
Ziad Majed, professor at the American University of Paris, said Washington has remained "ambiguous" over whether it wants Assad to stay or leave.
"The proof of sarin gas is a way of reminding everyone that he cannot be part of Syria's future," he said.
Washington also has painful memories dating back to February 2003 when then US Secretary of State Colin Powell brandished a vial at the United Nations supposedly containing Iraqi anthrax, paving the way for the US-led invasion.
No stockpiles of chemical, biological or other weapons of mass destruction were ever found.
"In some ways, the Syrian people are also paying the price of the war in Iraq and the manipulations at the time," said Emile Bitar, researcher at France's Institute of International and Strategic Relations.