The most senior Syrian politician to defect to the opposition has told the BBC the Bashar al-Assad regime will not hesitate to use chemical weapons if it is cornered.
Nawaf Fares, who is an ex-ambassador to Iraq, said unconfirmed reports indicate such weapons might have already been used.
He also said 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 Syria and the meeting comes amid mounting pressure for tougher international action against the country.