BEIRUT: A Syrian general and eight other soldiers were killed late Tuesday in a tunnel bomb outside Damascus, a monitoring group said.

The Syrian Observatory for Human Rights said rebel fighters planted explosives in a tunnel in the town of Harasta, northeast of Damascus.

"The explosion killed a Syrian officer at the rank of general, and eight other members of regime forces, and wounded several people," Observatory head Rami Abdel Rahman said.

The blast hit Harasta´s department of motor vehicles, where the group had been meeting.

"The building collapsed and there are still 15 people who are unaccounted for," Abdel Rahman told AFP, adding that the death toll was likely to rise as some of the wounded were in critical condition.

Harasta lies in Eastern Ghouta, a region east of Damascus that has long been a stronghold for rebel factions including the powerful Jaish al-Islam.

But government forces have made a major push in the area in recent weeks, despite a nationwide ceasefire in force since December 30.

On Tuesday, regime fighters seized a dozen farm fields from rebel groups in Eastern Ghouta and launched rockets into opposition-held territory in Harasta.

More than 310,000 people have been killed in Syria since conflict began in March 2011 with anti-government protests that were met with a regime crackdown.

In late December, Turkey and Russia brokered a truce deal that initially saw a decrease in violence in Syria.

But fighting has escalated in recent weeks across the country, including around Damascus and further north in the province of Aleppo.

Air strikes on the village of Kafr Halab on Tuesday left three civilians dead and wounded several other people, said the Observatory, which relies on a wide network of activists and fighters on the ground.