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.
He also said that major bombings across Syria had been orchestrated by the regime in collaboration with al-Qaeda.
Meanwhile, UN-Arab League envoy Kofi Annan is due to hold talks with Russian President Vladimir Putin on Syria.
Russia is a key ally of Syrian and the meeting comes amid mounting pressure for tougher international action on Syria, which has been in turmoil since March last year when an attempted uprising began.
The UN observer mission's mandate in Syria comes on to an end on Friday and a new UN resolution is needed to renew it.
Mr Fares said President Bashar al-Assad would not relinquish power peacefully.
He said he would only be ousted by force "even if he will have to eradicate the entire Syrian people".
Mr Fares was the most prominent politician to defect since the uprising against President Assad began.
He has held senior positions in the ruling Baath Party and powerful security services, and served as governor in several provinces.
He told BBC security correspondent Frank Gardner that the government "will inevitably fall".
"It is absolutely sure that this government will fall in a short time. We wish for this time to be short so that more sacrifices are reduced," he said.
Syria is known to have a significant stockpile of chemical weapons.
There have been growing concerns in neighbouring countries and in key Western governments about the security of such weapons should the regime fall.
Asked if he thought President Assad might us chemical weapons against the opposition, Mr Fares described him as "a fully-fledged criminal like a wounded wolf".
"There is information, unconfirmed information, that chemical weapons have been used in Homs," he said.
"I am convinced that if Bashar al-Assad's regime is further cornered by the people… he would use such weapons."
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.
Activists say that troops backed by armoured vehicles have entered the Midan district to try to dislodge rebels.