PARIS France's foreign minister said on Tuesday that there was no doubt the Syrian government had used nerve agent sarin against rebels, and that all options, including military action, were under consideration.
Increasing reports from the battlefield of the use of chemical weapons have lent urgency to a new diplomatic push to end the war and fuelled some calls for Western intervention in the conflict.
Speaking on France 2 television, Foreign Minister Laurent Fabius said some samples tested by Paris proved that the Syrian government had used sarin.
"In the second case there is no doubt that it was the regime and its accomplices because we are aware of the entire chain, from when the attack took place, to when the people were killed and when the samples were taken," he said.
A French diplomatic source said the blood and urine samples were taken after a Syrian government helicopter dropped munitions on April 29 at Saraqib near the northern city of Idlib.
France has been testing samples of suspected chemical weapon elements for several weeks, including some smuggled out by reporters from the French daily Le Monde, and others obtained from inside Syria.
However, the source said Paris could not determine from the Le Monde samples who was responsible for the use of sarin at Jobar, near central Damascus, between April 12-14.
The results were handed to the Swedish head of a U.N. chemical weapons investigation team, Ake Sellstrom, on Tuesday morning in Paris, Fabius said. Both Washington and Moscow were made aware of the results on Monday.
The source added that Paris was also testing samples from other suspected chemical attacks at different locations.
President Bashar al-Assad's government has denied using chemical weapons and has in turn accused rebels of deploying them in the two-year civil war that the United Nations says has killed more than 80,000 people.
RED LINE CROSSED?
When asked whether a red line had been crossed, Fabius said that "undoubtedly" a line had been crossed and that Paris was discussing with its allies how to react.
"All options are on the table," he said. "That means either we decide not to react or we decide to react including by armed actions targeting the place where the gas is stored."
He said the military option was not at the top of the list for now as it was still vital to ensure that efforts to reach a peaceful solution were not hindered.
The French source said Paris hoped the results, which it said were the first to fully comply with international standards, would help U.N. investigators push their case to enter Syria.
They have been ready for weeks, but diplomatic wrangling and safety concerns have delayed their entry into the country.
The source added that once investigators had completed their first report on the chemical weapons issue, France would push for action at the U.N. Security Council, where three resolutions have so far been vetoed by Russia and China.
"This is a way of adding pressure on Syria and those who support it," the source said. "I can't see how Russia could defend the use of chemical weapons."
While France backs proposed peace talks between the government and opposition to be held in Geneva, it has repeatedly said it would be pointless to have negotiations without clear parameters set beforehand.
"We'll give Geneva every chance of success. It can take a few days, a few weeks, but not six months (to put in place)," the source said.
Syria, which is not a member of the anti-chemical weapons convention, is believed to have one of the world's last remaining stockpiles of undeclared chemical arms.
"It would be unacceptable that those guilty of these crimes remain unpunished," Fabius said.
(Editing by Catherine Bremer and Mike Collett-White)