Syrian rebels are pressing their advance in the central province of Hama, as they try to take out its military airport.
"The rebels are now nine kilometres away from Hama military airport, which they want to put out of action," Rami Abdel Rahman of the Syrian Observatory for Human Rights said on Tuesday.
A rebel leader in the area, Yusef al-Hassan, said the airport was important because "that is where the regime makes its barrel bombs, and warplanes take off from there to carry out air strikes".
Barrel bombs have killed hundreds of civilians, especially in rebel areas of the divided northern city of Aleppo, in recent months.
According to the Observatory, rebels seized a major checkpoint north of Hama city, which is firmly under regime control, on Monday night.
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The takeover of the checkpoint in Tarabih comes on the back of Sunday's capture of a weapons depot in the area.
"The regime has suffered several defeats in Hama province in recent days," said Abdel Rahman.
As they have advanced, rebels have cut off the road linking Hama city, the provincial capital, to a string of regime-controlled Christian and Alawite villages in the west of the province, he added.
Hassan said the regime was sending reinforcements.
"They are stepping up their troop presence here, which will limit the regime's capabilities in other areas," the rebel leader said.
As for the military airport: "We are already striking it with Grad missiles," Hassan said.
Rights groups have hit out at the regime for using the crude bombs, which they describe as failing to discriminate between civilian and military targets.
A barrel bomb strike on a rebel-held village in Daraa province Monday killed an elderly man, his daughter and her three grandchildren, said the Observatory.
In Aleppo itself, rebels on Tuesday detonated two explosives-filled tunnels under a regime-held building, leaving "13 dead among the guards and regime forces" and wounding an unspecified number of others, the Observatory said.
The building in Aleppo's mostly regime-controlled old city was a police station occupied by regime forces.
The Islamic Front, one of the largest rebel groupings, said it launched the attack.
A photograph posted by the group on Facebook reportedly of the attack showed a huge cloud of smoke rising into the sky near to the city's historic citadel.
