Russian forces moved into an opposition enclave in the Syrian city of Deraa on Tuesday to try to avert an army assault on a stronghold that has defied state authority since it was retaken three years ago, witnesses, residents, and army sources said.

Their entry brought a halt to shelling by pro-Iranian army units who have encircled the enclave, where protests first erupted in 2011, and had attempted to storm the area on Monday in the latest drive to force former rebels to surrender.

The Syrian army, aided by Russian air power and Iranian militias, in 2018 retook control of the province of which Deraa is the capital and which borders Jordan and Israel's Golan Heights.

Local officials and army sources say the Iranian-backed army units have been pushing for a major new offensive.

However, Moscow gave guarantees to Israel and Washington in 2018 that it would hold back Iranian-backed militias from expanding their influence in the strategic region.