Syrian rebels fully captured a northern town near the Turkish border on Tuesday after weeks of siege and heavy fighting, activists said.

The takeover of Harem, a town of 20,000 in northern Idlib province, was the latest in a string of recent rebel successes that include the capture of wide areas along the border with Turkey. Most of those areas have been in northern Aleppo province, where anti-government forces have captured at least three large military bases.

The Britain-based Syrian Observatory for Human Rights said the rebels captured Harem in the early hours of Tuesday. Mohammed Kanaan, an Idlib-based activist, said the last post to be taken was the historic citadel, which overlooked the town. The army had turned the citadel into a military post.

"Harem is fully liberated now," Kanaan he said via Skype. He added that as the rebels pounded army posts and checkpoints in Harem, the troops withdrew to the citadel that later fell in the hands of rebels.

In his traditional Christmas address, Pope Benedict XVI decried the slaughter of the "defenceless" in Syria, where anti-regime activists estimate more than 40,000 have died in fighting since the uprising began in March 2011.

The Pope encouraged Arab spring nations, where long-serving dictators were forced to step down.

Supplies difficult to deliver

In Aleppo province, which neighbours Idlib, local activist Mohammed Saeed said rebels attacked a military base in the town of Mannagh near the border with Turkey. He said it is one of four air bases in the province.

Regime forces have been using helicopters to carry supplies to besieged areas and attack rebel positions.

The regime has had increasing difficulty sending supplies by land to Aleppo province after rebels captured in October the strategic town Maaret al-Numan. The town is on the highway that links Damascus with Aleppo, Syria's largest city and commercial centre and a major battleground in the civil war since July.

"Airplanes and helicopters are the only way to send supplies since the Free Syrian Army controls the land," Saeed said. He added that rebels are also laying a siege to Aleppo's international airport known as Nairab and threatening to shoot down military or civilians planes using it.

In the Damascus suburb of Jaramana, opposition gunmen ambushed the head of military intelligence in the area and seriously wounded him. He later died of his wounds, the Observatory said.