Syria has threatened to use its chemical and biological weapons in case of a foreign attack, the first time it has admitted having weapons of mass destruction.
The Foreign Ministry said it would not use its the arms against its own citizens.
The announcement came as Syria faces international isolation, a tenacious rebellion that has left at least 19,000 people dead and threats by Israel to invade to prevent such weapons from falling into rebel hands.
Syria's decision to reveal the long suspected existence of its chemical weapons suggests a desperate regime deeply shaken by an increasingly bold rebellion that has scored a string of successes in the past week, including a stunning bomb attack that killed four high-level security officials, the capture of several border crossings and sustained offensives on the regime strongholds of Damascus and Aleppo.
"No chemical or biological weapons will ever be used, and I repeat, will never be used, during the crisis in Syria no matter what the developments inside Syria," a Foreign Ministry spokesman said.
"All of these types of weapons are in storage and under security and the direct supervision of the Syrian armed forces and will never be used unless Syria is exposed to external aggression."
Syria is believed to have nerve agents as well as mustard gas, Scud missiles capable of delivering the chemicals and a variety of advanced conventional arms, including anti-tank rockets and late-model portable anti-aircraft missiles.
Israel has said it fears that chaos following president Bashar Assad's fall could allow the Jewish state's enemies to access Syria's chemical weapons, and has not ruled out military intervention.
Meanwhile state TV showed videos of sweeps by Syrian militia through Damascus neighbourhoods once held by rebels, kicking down doors and searching houses in mop up operations against the fighters that had managed to hold parts of the capital for much of last week.
It was a different story in Aleppo, however, where the Britain-based Syria Observatory reported fierce fighting.
Aleppo, Syria's biggest city with about three million residents, has been the focus of rebel assaults by a newly formed alliance of opposition forces called the Brigade of Unification. The group said it was launching an operation to take the city.
Even as the government appeared to be reasserting control in the capital after the weeklong rebel assault, the Arab League offered Assad and his family a "safe exit" if he steps down.
"This request comes from all the ... Arab states: Step aside," said Qatari Prime Minister Hamid bin Jassim Al Thani at an Arab League foreign ministers meeting.
He urged Syria to form a temporary transitional government to plan for a possible post-Assad era.
The Arab League has already suspended Syria's membership and it is doubtful that Assad will pay much attention to their calls. He ignored a similar request to step down in exchange for asylum by Tunisian President Moncef Marzouki last February.