The former head of the UN observer mission in Syria says it is "only a matter of time" until President Bashar al-Assad's government falls.
But Norwegian Gen Robert Mood, who left Syria last week, said Assad's fall would not necessarily mean an end to the 16-month-old conflict.
Meanwhile, Syrian forces renewed their assault on the northern city of Aleppo today.
The US state department says it fears Syrian government forces are preparing to carry out a massacre there.
The pro-government al-Watan newspaper warned that the "mother of all battles" was about to start.
Separately, UN High Commissioner for Human Rights Navi Pillay appealed to both sides to spare civilians, citing concerns of "the likelihood of an imminent major confrontation".