DAMASCUS, May 23: Syrian forces tried to storm the rebel bastion of Rastan on Wednesday under cover of heavy gunfire, shelling and rocket bombardment, reports said, as Damascus admitted sanctions were biting hard.

The rebel Free Syrian Army, meanwhile, denied it was behind the kidnapping of Lebanese Shia pilgrims in the north, an incident adding to tensions in neighbouring Lebanon which is already divided between pro- and anti-Damascus camps.

There was no word on any Rastan casualties, but the Syrian Observatory for Human Rights said 12 people were killed nationwide, including seven troops shot dead at Qalamun in Damascus province as they tried to defect to the rebellion.

Soldiers were trying to overrun Rastan for the second time in 10 days, with shells crashing into the town at the rate of “one a minute” at one stage, according to the Britain-based watchdog.

An activist said that Free Syrian Army fighters were defending Rastan's entrances but that “regime forces are being strengthened with new deployments,” including from the elite Republican Guard.

“Electricity has been cut off in Rastan, and water tanks have been shelled,” said activist Abu Rawan. “There is also a severe lack of food because the market is closed and we can't bring food in from nearby villages.”

Hours later, the activist said the army assault eased when a team of UN observers entered Rastan.

“The situation is calm now because the UN monitors have arrived” having heard the shelling, Abu Rawan said, adding, however, “God protect us when they leave.”

On May 14, 23 soldiers were killed in a failed assault on the town, which straddles the main highway linking the capital to the north and where rebels regrouped from the battered city of Homs.

Elsewhere, troops fired on protesters in Syria's second city Aleppo as about 1,500 people rallied against the regime, triggering armed clashes, said the Observatory, without providing any details on casualties.

Activists said lawyers and sympathisers with the revolt staged a sit-in at Aleppo's judicial complex to demand the release of political prisoners, as well as pay tribute to four students killed at a May 3 rally in the northern city.

The uprising against President Bashar al-Assad broke out with peaceful democracy protests in March 2011, prompting a fierce crackdown.

More than 12,600 people have been killed in the bloodshed, nearly 1,500 of them since a UN-backed truce took effect April 12, according to Observatory figures.—AFP