The United Nations Security Council is to hold an emergency meeting over reports by Syrian rebels that hundreds of people have died in a chemical weapons attack by government forces outside the capital, Damascus.
The Syrian government denies the reports.
Videos posted online showed lifeless bodies with no marks indicating exterior injuries.
The BBC reports the videos cannot be independently verified.
Rebels say rockets with toxic agents were launched at suburbs in the Ghouta region early on Wednesday.
The Syrian army says the accusations were fabricated to cover up rebel losses.
United Nations chemical weapons inspectors arrived in Syria on Sunday with a mandate to investigate three locations where there have been accusations that chemical weapons were used.
Britain and France want the inspectors to be allowed immdiate access to the site of the latest claims.
Prof Alexander Kekule, of the Institute for Medical Microbiology at Halle University in Germany, told the BBC that one of the videos - although of poor quality - was consistent with the aftermath of an attack with a chemical agent.
But he added that none of the patients showed typical signs of sarin or other organophosphorous nerve agents, or signs of blistering agents.
"It also cannot be totally excluded that the whole video is a political staging. In this case, however, it would be a very good one," he said.
The BBC reports both the rebels and government forces have previously accused each other of using chemical weapons.