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.
Former ambassador to Iraq Nawaf Fares says unconfirmed reports indicate such weapons might have already been used.
He also says major bombings across Syria had been orchestrated by the regime in collaboration with al-Qaeda.
Mr Fares, who defected last week from his post as ambassador in Baghdad, compared Syria's rulers to a wounded wolf that would do anything to survive.
He believes the president will only be removed from power by force.
Meanwhile, fighting in Syria is moving closer to the centre of the capital, Damascus.
Government troops and vehicles have been used in the district of Maidan after two days of clashes between government forces and rebels in the south of the city.
Activists say clashes are now happening in the north of the city.
At least 10 people are believed to have been killed.
It's the worst fighting reported in the capital since an anti-government uprising began last year.
American Secretary of State Hillary Clinton says events in Syria, including defections and intensified fighting in Damascus, are a sign Bashar al-Assad's government is under intense pressure and will not survive.
Mrs Clinton says if China and Russia were to put pressure on Mr Assad, it would have a direct impact.