Syria said on Monday it would not use chemical weapons against its own people after the United States warned it would take action against any such escalation.
The statements came amid media reports, citing European and U.S. officials, that Syria's chemical weapons had been moved and could be prepared for use in response to dramatic gains by rebels fighting to topple President Bashar al-Assad.
"Syria has stressed repeatedly that it will not use these types of weapons, if they were available, under any circumstances against its people," the foreign ministry said.
U.S. Secretary of State Hillary Clinton had earlier warned that Washington would take action if Syria used the weapons.
"I am not going to telegraph any specifics what we do in the event of credible evidence that the Assad regime has resorted to using chemical weapons against their own people, but suffice to say, we are certainly planning to take action if that eventuality were to occur," she said during a visit to Prague on Monday.
The opposition believes that Assad, who has upped his response to rebel gains in the 20-month-old revolt, could turn to heavier weapons and some have suggested he might use chemical weapons.
The rebels have begun to advance quickly in recent weeks after months of slow sieges to cut off army routes and supplies.
In the past few weeks, they seized several military bases around the country, and an oil field and hydro-electric dam in the northeast. Rebels are using anti-aircraft weapons to attack the military helicopters and fighter jets that have bombarded their positions with impunity until now.
The main focus for the army in the past five days has been Damascus, where security forces are pushing back hard against the rebels and trying to seal the capital off from rebel-dominated suburbs.
The opposition-linked Syrian Observatory for Human Rights said the Syrian army was trying to take over Daraya, on the southern outskirts of Damascus, and was attacking rebels with rockets as it advanced into some parts of the town.
A Syrian security source said that the army had blocked three entrances into Daraya and was optimistic it could take the town. Rebels said they would be able to hold their ground.
"There have been several attempts to storm Daraya and each time the army has suffered major losses. This is not new," said activist Samir al-Shami, of the Syrian Youth Union in Damascus.
Other activists reported heavy bombardment of the towns of Deir al-Asafir and Beit Saham, which are close to the highway leading to Damascus International Airport, the scene of three days of heavy clashes that effectively closed the airport.
EgyptAir said it had resumed flights after a three day suspension, saying the situation around the airport was now stable. All other airlines contacted said their flights were still suspended, citing concerns by local staff that the road was still unsafe.
Rebels had been planning an advance on the capital, Assad's power base.
The army struck back around the airport last Thursday and since then the suburbs of Damascus have been rocked by fierce clashes and heavy shelling. Activists described continuous shelling that killed more than 56 people around Damascus. More than 200 people died across Syria on Sunday, according to the Observatory.
Neither side has the upper hand in the fighting around Damascus. A previous attempt by rebels last July to hold ground in the city was crushed, but the fighters fell back into the suburbs and nearby countryside.
The Observatory reported air and artillery bombardment in towns across Syria on Monday. An air strike on the northern border town of Ras al-Ain, which it said killed at least 12 people and wounded more than 30, prompted Turkey to scramble fighter jets along the border. [ID: nL5E8N3792]
More than 40,000 people have died in the conflict, with hundreds more killed each week.
© 2015 Thomson/Reuters. All rights reserved.