The alleged poison gas attack in the Syrian town of Douma, said to have killed at least 60 people and injured more than 1,000, has thrust the country's conflict back in the international spotlight.
But did it really happen?
"You need the evidence from on the ground. It's quite difficult really from images," Alastair Hay, Professor of Environmental Toxicology at the University of Leeds in England, told Euronews.
"They give you an impression and you can form a picture but really for the convincing evidence you need something on the ground. You need interviews with victims, you need photographic evidence of maybe damage to vegetation, which chlorine will cause, images or reports of what the smell of the agent was, what the effect was on people. You need to talk to doctors as well."
"Barbaric" and "outrageous"
The US is talking to Britain and France how about to respond to the alleged attack, as it considers possible military action. In Brussels, there's a push for political pressure.
"After the last outrageous use of chemical weapons in Syria there was a military response by the United States and now we see the situation that once again chemical weapons are being used by the Assad regime," said David McAllister, Chair of the European Parliament Foreign Affairs Committee.
"I believe we have to use all political, all diplomatic channels to increase the political pressure on the regime in Damascus that this has to stop. This is a barbaric outrageous behaviour and this is not only a question for us in the European Union, and the United States, and other western countries, this is also a question for Russia and Iran."
Syrian refugee skeptical
Mohamad Blakah, from Damascus, is now a refugee in Belgium. An activist and researcher, he left Syria in late 2011. He told Euronews that he's skeptical about the international community's response to Douma.
"Do they want to do something just to show the world that we don't allow this and we want to save our faces, we don't want to be ashamed or they want really to punish Assad," he asked.
"This is the question. And I don't think that they want to punish Assad because if they want to they should have done it a long time ago, years ago."
London and Paris are stressing that who's to blame for the alleged attack in Douma stills needs confirming.