Al Jazeera reported on Tuesday that the Syrian ambassador to Cyprus, Lamia al-Hariri, had defected and left for Qatar.

Meanwhile, clashes broke out in Syria's second-largest city of Aleppo Tuesday, opposition activists said, as the regime's helicopter gunships shelled areas on the outskirts captured by rebels.

Al-Hariri becomes the second Syrian diplomat to leave her post, after Nawaf Fares, the ambassador to Iraq, defected earlier in July. He was also reported to be in Qatar.

The opposition Syrian Observatory for Human Rights reported fierce fighting in an increasing number of districts in Aleppo. Government forces were also seeking to quell a mutiny in the city's central prison, where eight people were killed, the Observatory said.

The rebel Free Syrian Army (FSA) described the mutiny as "the first step towards the liberation" of Aleppo.

"Helicopter and tank shells are falling on areas in the outskirts of Aleppo, which came under the control of the rebels," activist Abu Haytham al-Halabi told dpa by phone.

"On the ground, troops were defeated by the rebels but they are now using their helicopters to bombard those areas," he said.

The offensive in Aleppo came as the FSA warned that President Bashar Assad's regime had moved chemical weapons to airports near Syria's borders.

"Most of us in the Free Syrian Army command know very well where these weapons are located," Colonel Kassim Saadeddine told Al Jazeera.

"And now we have solid information that Assad has transferred some of these weapons with the equipment for mixing chemical components to airports near the border," he added.

Syria has threatened that it could use chemical or biological weapons against "external aggression," but not against its own people.

Syrian Foreign Ministry spokesman Jihad Makdisi said Monday that such weapons would "never be used unless Syria is exposed to external aggression."

Makdisi emphasized that as long as the country's 16-month uprising remained an internal affair, the weapons would not be used: "Any chemical or biological weapons will never be used during the crisis in Syria, however that crisis develops within Syria."

His comments sparked international condemnation. US President Barack Obama said: "The world is watching, and they will be held accountable to the US and the international community should they make the tragic mistake of using those weapons."

On Tuesday, a senior Israeli defence official said Syria's stockpiles of chemical weapons was "under the full control" of the Assad regime.

"At the moment, the Syrian regime is fighting for its very existence, but all of its chemical weapons and its weapons of mass destruction are under full control of the regime," the head of the Defence Ministry's diplomacy and security bureau, Reserve Major General Amos Gilad, told public radio.

Syrian state television played down Makdisi's previous comments, quoting a new statement Tuesday that Syria would "never use chemical and biological weapons ... and if such weapons exist, it is natural for them to be stored and secured."

In the capital Damascus, the army pushed into dissident districts in the south, entering the Kaddam and al-Assali areas where they carried out raids and arrests, the Observatory said.

The London-based group put Tuesday's death toll across the country at 48 by mid-afternoon.

Many Damascus residents remain displaced by the recent fighting and were in need of humanitarian assistance, the International Commission of the Red Cross (ICRC) said.

"Although the situation has calmed down in some parts of the city, life is not back to normal," said Marianne Gasser, the ICRC's head of delegation in Syria. "People who have fled their homes only want to be able to go back. Unfortunately, for many, there has not yet been any opportunity to do so."

Meanwhile, the opposition Syrian National Council (SNC) denied media reports that it would accept a transitional government led by a regime member if Assad stepped down.

"Only a person whose hands were not stained with blood would be accepted in a joint government made up of members of the opposition and the Free Syrian Army, and this will only happen if Assad leaves power for good," Naji Tayyara, an SNC member, told dpa by phone.