Some 3,600 patients with neurotoxic symptoms were treated this week at three hospitals in Syria's Damascus region, 355 of whom died, Geneva-based Medicins Sans Frontieres, or Doctors Without Borders, said Saturday.

Syria's opposition on Wednesday said government forces killed at least 1,300 people in a chemical weapons attack in the Ghouta region, east of Damascus, an accusation immediately denied by President Bashar al-Assad's government.

"Medical staff working in these facilities provided detailed information to MSF doctors regarding large numbers of patients arriving with symptoms including convulsions, excess saliva, pinpoint pupils, blurred vision and respiratory distress," Dr. Bart Janssens, MSF director of operations, said in a statement.

MSF personnel have not been able to visit the hospitals in question due to a lack of security.

The patients suffering from those symptoms were mainly administered atropine, a medicine used to treat victims of chemical weapons attacks.

Supplies of the drug ran out and MSF is now trying to replenish them, he said.

MSF has collaborated closely since 2012 with a network of hospitals and medical services run by the Damascus regional government, providing medicine, medical equipment and technical support.

Syrian Information Minister Omran al-Zoubi said Saturday that troops loyal to President Bashar al-Assad "have not used nor will use" chemical weapons.

He also echoed an accusation made by the Syrian army that the rebels used chemical agents in clashes Saturday with government forces outside Damascus and poisoned roughly a score of soldiers.

Separately, a car-bomb blast in downtown Damascus Saturday left at least five dead and 25 wounded, Syrian security forces told Efe.

The Obama administration has said the use of chemical weapons by the Syrian government would constitute the crossing of a "red line" that could trigger potential U.S. military action.

More than 100,000 people have died since Syria's civil war broke out in March 2011, the United Nations said late last month. EFE