Syrian government forces on Monday seized control of a strategic area outside Damascus used by rebels to fire mortar shells at the capital, state media and a monitor said.

State television broadcast live images from Dakhaniyeh, southeast of Damascus, and the Syrian Observatory for Human Rights confirmed that "rebels have withdrawn".

The capture comes nearly a month after government forces launched an offensive to regain control of the area, from which rebels have launched mortar shells against the Old City of Damascus and the pro-regime Jaramana district outside the capital.

The army "restored security and stability to Dakhaniyeh and its surroundings," state television said, adding that "a large number of terrorists" were killed.

A security source said the capture would allow government troops to "tighten the noose on terrorist groups in Ain Tarma and Jobar," two areas around the capital under rebel control.

Both Ain Tarma and Dakhaniyeh are in the Eastern Ghouta area, which is a stronghold of rebels in Damascus province.

"The operation in Ghouta will continue until it is completely cleared of any terrorist presence," the security source said.

The Observatory said four regime soldiers had been killed entering Dakhaniyeh by a bomb planted by rebels inside the area.

The capture follows a string of victories for regime forces in the area around Damascus, where they have retaken several rebel strongholds in recent months.