Elite government forces backed by Hezbollah converged Tuesday, July 8 on the north Syrian city of Aleppo as rebels bolstered their own fighters in readiness for a major showdown, a monitor said, Agence France-Presse reported.

Rami Abdel Rahman of the Syrian Observatory for Human Rights said it was likely that pro-regime forces were preparing to lay siege to rebel-held parts of Aleppo, the country's pre-war commercial capital.

The rebels fighting to oust President Bashar al-Assad have controlled parts of the northern city since they wrested them from the government's hands in July 2012.

"Commando troop reinforcements from the Republican Guard and from (Lebanon's) Hezbollah continued to be sent, in a bid to surround Aleppo city," the Observatory said.

At the same time, "rebel and (allied) Islamist brigades sent reinforcements of their own... through the eastern entrance to Aleppo city," added the Britain-based organisation.

Aleppo was Syria's most populous city before the conflict, but it is now a major battle zone split into areas controlled by the rebels concentrated in the east and those held by the government mainly in the west.

The rebel-held areas have come under daily aerial bombardment since December.

The Observatory says the offensive has killed some 2,000 civilians, including more than 500 children, since January. It has also forced tens of thousands of families to flee.