The US-backed Syrian Democratic Forces (SDF) said they had made further gains against IS a day after announcing an operation to capture northern and eastern parts of Deir al-Zor province.
Around 590,000 people are now living in besieged areas of Syria, according to UN figures.
"They attack us politically and then they send officials to deal with us under the table, especially the security, including your [the Australian] government," Assad was quoted as saying.
Intra-Syrian negotiations will continue in Geneva through the beginning of next week.
Emboldened by the Russian intervention, Syrian President Bashar Assad has been regaining ground against the multitude of fractioned and unaligned rebel groups.
US officials have long played down the idea that Assad's forces would turn their sights on the US-backed Syrian rebels, but they cannot rule out the possibility.
US Defense Secretary Ashton Carter admits the number is much smaller than expected, after the Pentagon initially proposed a training program targeting 5,000 soldiers per year.
Mob attacks ambulance carrying two Syrians brought into Israel for medical treatment, killing one and leaving the second badly wounded.
Just four months ago it was the army and its allied militia that were launching a major bid to besiege rebel-held areas of eastern Aleppo. Now, rebels are claiming the initiative.
“We extend to you and the great leadership of the Israeli people our warmest congratulations and blessings in the democratic wedding witnessed by the State of Israel.”