Syria admitted on Monday it possesses chemical weapons and warned it would use them if attacked by foreign powers though not against its own people, as regime troops battled rebels in Damascus and Aleppo.
The warning by foreign ministry spokesman Jihad Makdissi comes amid growing international concern that Damascus is preparing to deploy its chemical arsenal in the repression of a 16-month uprising against President Bashar al-Assad.
"Syria will not use any chemical or other unconventional weapons against its civilians, and will only use them in case of external aggression," Makdissi told a media conference in Damascus.
"Any stocks of chemical weapons that may exist, will never, ever be used against the Syrian people," he said, adding that in the event of foreign attack, "the generals will be deciding when and how we use them."
Makdissi's comments come a day after the United States said it would "hold accountable" any Syrian official involved in the release or use of the country's chemical weapons.
Israel also said on Sunday it was concerned chemical weapons might land in the hands of the Lebanese Shiite militia Hezbollah.
The spokesman also said Syria firmly rejected a demand by the Arab League that Assad step down.
"We are sorry that the Arab League has descended to this level concerning a member state of this institution," he said.
"This decision only concerns the Syrian people, who are the sole masters of the fate of their governments."
A meeting late Sunday in Doha of Arab League foreign ministers issued a statement calling on Assad to "renounce power," promising that he and his family would be offered "a safe exit."
"There is agreement on the need for the rapid resignation of President Bashar al-Assad," Qatar's Prime Minister Sheikh Hamad bin Khalifa Al-Thani told journalists after the meeting wound up in the small hours of Monday.
Makdissi also vowed that Syrian forces would soon regain control of several border posts that rebel forces seized along the frontier with Iraq and Turkey.
The rebels "will not hold onto them and they will be gone in a few days," he said.
Jittery residents, meanwhile, reported hearing gunfire and explosions into the early hours of Monday morning in the upscale Mazzeh neighbourhood of west Damascus, while activists reported shelling in several other flashpoint neighbourhoods.
Syrian state television reported an assault on Mazzeh, calling the operation "targeted and quick."
The broadcaster showed footage of troops firing as they entered part of the neighbourhood and featured an interview with one soldier.
Regime forces also "chased the remnants of the terrorists in Barzeh," in the northeast of Damascus, the report said.
The Syrian Observatory for Human Rights said the government offensive in Barzeh was being spearheaded by "the feared Fourth Brigade" commanded by Assad's powerful younger brother Maher and has sparked a mass exodus of residents.
The Britain-based watchdog said at least 23 people were "summarily executed" by regime forces in Damascus.
"Sixteen people, most of them younger than 30, were summarily executed by shooting on Sunday in Mazzeh," Observatory chief Rami Abdel Rahman said. Seven others were executed in a similar fashion in Barzeh.
It was unclear whether the executions were of civilians or rebels fighters.
The heads of two of the victims had been crushed by vehicles, and one was shot through the eye, Abdel Rahman said.
Three of the dead were found with their hands tied, and the bodies of some had been pierced by bayonets, he added.
The Local Coordination Committees, a grassroots network of activists inside Syria, reported that military reinforcements were sent during the night to a number of Damascus neighbourhoods rocked by clashes since the rebels announced the launch of "Operation Damascus Volcano" a week ago.
The LCC also reported fierce clashes during the night and into the morning between rebel forces and Syrian troops in the northern city of Aleppo, where the rebel Free Syrian Army says a war of "liberation" is underway.
Largely excluded from the violence and protests of the country's 16-month uprising until recently, Aleppo has emerged as a new front in the battle between rebel fighters and Assad's troops.
The Observatory said the death toll in fighting across Syria on Sunday stood at 123, including 67 civilians, 22 rebels and 34 soldiers.
The watchdog group said that more than 19,000 people have been killed since the uprising against Assad's regime began in March 2011.
Fighting has intensified since a Wednesday bombing that killed national security chief General Hisham Ikhtiyar, Defence Minister General Daoud Rajha, Assad's brother-in-law Assef Shawkat and General Hassan Turkmani, head of the regime's crisis cell on the uprising.
The EU meanwhile beefed up sanctions against Assad's regime on Monday and agreed to tighten an arms embargo by inspecting vessels and planes suspected of carrying arms, diplomats in Brussels said.
EU foreign ministers began talks in Brussels with an agreement to freeze the assets of 26 Syrians and three firms close to the Assad regime in the 17th round of sanctions since protests erupted last year, diplomats said.