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link to www.bbc.co.uk]
The most senior Syrian politician to defect to the opposition has told the BBC the regime will not hesitate to use chemical weapons if it is cornered.
Nawaf Fares, ex-ambassador to Iraq, said unconfirmed reports indicated such weapons might have already been used.
The comments were made as clashes were reported in Baghdad Street, central Damascus, and fighting spread in suburbs around the city.
Syria peace envoy Kofi Annan is due to hold talks with Russia's president.
Russia is a key ally of Syria and the meeting comes amid mounting pressure for tougher international action against the country.
Syria is known to have a significant stockpile of chemical weapons. There have been growing concerns in neighbouring countries and among Western governments about the security of such weapons should the regime fall.
Asked if he thought President Assad might use chemical weapons against the opposition, Mr Fares told BBC security correspondent Frank Gardner in an interview in Qatar that he would not rule it out, describing Mr Assad as "a wounded wolf and cornered".
"There is information, unconfirmed information of course, that chemical weapons have been used partially in the city of Homs," he said.
Violence is continuing to spread across the country and in the capital Damascus as rebels - now better equipped and more organised - confront the army and government-backed militia.
Witnesses say the capital is currently seeing the biggest military deployment in the 16-month uprising.
Clashes were reported in Baghdad street, central Damascus. AFP news agency said machine-gun fire was heard in nearby Sabaa Bahrat square, site of the country's Central Bank.
Activists reported continued clashes on the south-western side of the city, and said fighting had broken out on the other side, at Barzeh and Qaboun. Attack helicopters were seen there firing rockets for the first time since the uprising began.