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 has been in turmoil since March last year when an uprising against the government of President Bashar al-Assad began.
UN Secretary General Ban Ki-moon is due in Beijing for talks with the Chinese leadership, which has joined Russia in vetoing sanctions.
Diplomat[ic] efforts come as UN officials complained of huge obstacles put in the way of its aid operation in Syria.
'Wounded wolf'
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". » | Tuesday, July 17, 2012
