Both sides in the conflict are accusing the other of using a chemical weapon in a neighborhood outside of the city of Aleppo.
A reporter interviewed by Reuters seems convinced that some kind of chemical device was employed:
A Reuters photographer said victims he had visited in Aleppo hospitals were suffering breathing problems and that people had said they could smell chlorine after the attack.
"I saw mostly women and children," said the photographer, who cannot be named for his own safety.
"They said that people were suffocating in the streets and the air smelt strongly of chlorine."
The photographer quoted victims he met at the University of Aleppo hospital and the al-Rajaa hospital as saying: "People were dying in the streets and in their houses."
President Bashar al-Assad, battling a two-year-old uprising against his rule, is widely believed to have a chemical arsenal.
Syrian officials have neither confirmed nor denied this, but have said that if it existed it would be used to defend against foreign aggression, not against Syrians. There have been no previous reports of chemical weapons in the hands of insurgents.
Information Minister Omran al-Zoabi said rebels fired a rocket with chemical weapons at the town of Khan al-Assal, southwest of Aleppo, in what he called a "dangerous escalation".
He said the rocket had been launched from Aleppo's southeastern district of Nairab, part of which is rebel-held.
But a senior rebel commander, Qassim Saadeddine, who is also a spokesman for the Higher Military Council in Aleppo, denied this, blaming Assad's forces for the alleged chemical strike.
"We were hearing reports from early this morning about a regime attack on Khan al-Assal, and we believe they fired a Scud with chemical agents," he told Reuters by telephone from Aleppo.
U.S. President Barack Obama, who has resisted overt military intervention in Syria's two-year-old civil war, has warned Assad that any use of chemical weapons would be a "red line".
Don't worry. Obama won't declare that a "red line" has been crossed unless there are a lot more casualties than the official count of 25 dead in Aleppo. And it will have to be 100% clear that the Assad regime launched the weapon.
Even then, it is doubtful we will send any US assets to fight Assad without UN permission. And that will never come.