The humanitarian organisation said patients had arrived in three hospitals in the Damascus area on August 21 - when opposition activists say chemical attacks were launched against rebels.
MSF said staff at the hospitals described a large number of patients arriving with symptoms including convulsions, extreme salivation, contracted pupils, and sight and respiratory problems. The charity said many were treated with atropine, a drug administered to those with neurotoxic symptoms. The organisation said that while it cannot scientifically confirm the cause of the symptoms, they "strongly suggest" the use of a nerve agent.
Meanwhile, Syrian television yesterday claimed that government troops have found chemical agents in rebel tunnels in a Damascus suburb. There were also claims that some soldiers were "suffocating" in the tunnels, intensifying a dispute over blame for a gas attack that killed hundreds.
The claims came as the United Nations' leading disarmament official arrived in Damascus to seek access for inspectors to the site of the attack, and American president Barack Obama met with his national security advisers to discuss reports that it was the Syrian government which used chemical weapons.
Obama has been reluctant to intervene in Syria's civil war. But a year ago he said chemical weapons would be a "red line" , and he is under pressure to take action. A White House official said last week: "We have a range of options available."
The US Navy repositioned a ship armed with cruise missiles in the Mediterranean on Friday. But officials cautioned that Obama had made no decision on any military move against Syria.
American and European security sources said intelligence agencies have made a preliminary assessment that chemical weapons were used by Syrian forces in the attack near Damascus this week.
Syrian opposition accounts say that anywhere from 500 to well over 1000 civilians were killed by gas in munitions they say were fired by forces loyal to president Bashar al-Assad. Photographs and video footage of victims' bodies have heightened calls in the West for a robust response.
In a clear attempt to strengthen the government's denials of responsibility for the suspected chemical assault, Syrian state television said soldiers discovered chemical agents in rebel tunnels in the Damascus suburb of Jobar.
"Army heroes are entering the tunnels of the terrorists and saw chemical agents," it quoted a "news source" as saying. "In some cases, soldiers are suffocating while entering Jobar. Ambulances came to rescue the people suffocating in Jobar."
An army unit was preparing to storm the insurgent-held suburb, the report added.
Syrian opposition activists have accused Assad's forces of firing nerve-gas projectiles into Jobar and other rebellious suburbs before dawn on Wednesday. Later in the week, activists smuggled out tissue samples from victims of the attack.
The Syrian government said it would never use chemical weapons against its citizens. Assad's government has suggested rebels may have carried out the attack themselves to provoke foreign intervention.
Major world powers - including Russia, Assad's main ally, which has long blocked UN-sponsored intervention against him - have urged the Syrian leader to co-operate with a UN inspection team that has arrived to pursue earlier allegations of chemical weapons assaults in the civil war.
Angela Kane, the UN High Representative for Disarmament Affairs, arrived in Damascus yesterday to press for permission for inspectors to examine areas of the city said to have been targeted on Wednesday.
Obama has called the incident a "big event of grave concern" and one that demanded US attention, but said he was in no rush to get war-weary Americans "mired" in another Middle East conflict.
His caution contrasted with calls for action from Nato allies, including France, Britain and Turkey, where leaders have little doubt that Assad's forces had staged the pre-dawn missile strikes in Damascus.