Syria's chemical arsenal - Times LIVE

Pressure on President Bashar al-Assad has increased dramatically in the past week, with a rebel offensive in the two biggest cities and a devastating bomb attack that killed four members of Assad's inner circle in Damascus.

Assad's forces have launched fierce counter-offensives, reflecting his determination to hold on to power even at great cost, He has dismissed an Arab League offer to grant him a safe exit in return for a swift step down.

Foreign Ministry spokesman Jihad Makdissi said the army would not use chemical weapons to crush rebels, but they would be used against forces from outside the country.

"Any chemical or bacterial weapons will never be used ... during the crisis in Syria regardless of the developments," Makdissi said.

"These weapons are stored and secured by Syrian military forces and under their direct supervision and will never be used unless Syria faces external aggression."

Damascus has not signed a 1992 international convention that bans the use, production or stockpiling of chemical weapons, but officials in the past have denied that it had stockpiles.

As violence intensifies in Syria, insurgents have said they fear that Assad's forces will resort to non-conventional weapons as they try to claw back rebel gains across the country.

Western countries and Israel have expressed fears that chemical weapons will fall into the hands of militant groups as Assad's authority erodes.

Defying Arab League foreign ministers who on Sunday offered Assad a "safe exit" if he stepped down swiftly, the Syrian leader has waged a counter-attack in the capital to defeat rebels district by district.

Arab League ministers meeting in Doha urged the opposition and the rebel Free Syrian Army to form a transitional government, Qatari Prime Minister Sheikh Hamad bin Jassim al-Thani said in Doha.

Makdissi condemned calls for Assad to step down at a meeting of Arab foreign ministers in Qatar at the weekend, calling it a "flagrant intervention" in Syria's internal affairs.

"We regret that the Arab League stooped to this immoral level in dealing with a founding member instead of helping Syria," he said.

The Syrian army yesterday shelled rebel forces in the northern city of Aleppo and stormed the southern Damascus neighbourhood of Nahr Aisha, breaking into shops and houses and burning some of them, activists said.

Video clips showed dozens of men in green army fatigues massing in the neighbourhood, which looked abandoned.

Men carrying machine guns and rocket-propelled grenade launchers knocked and then kicked down doors and climbed through windows.

Assad's forces have reasserted control over several Damascus areas since they regained control of the central Midan district on Friday, following a devastating bomb attack that killed four of Assad's top security men.