Rebels in Syria’s north-western Idlib province advanced on Monday, seizing several army checkpoints as they inched closer towards taking over two major bases, a monitor and activists said.

The rebel advance in the northwest of Syria comes as Jabhat al-Nusra claim responsibility for two car bomb attacks that killed 12 people on Sunday in the central city of Homs.

A Twitter account purportedly managed by Jabhat al-Nusra carries a message claiming responsibility for the double car bomb attack in al-Zohra district of Homs on Sunday, including several pictures apparently showing the aftermath of the attack.

The Syrian Observatory for Human Rights also reports that rebels, including fighters from al-Nusra, took over a checkpoint “west of the town of Khan Sheikhun after fierce battles against regime troops.”

The Syrian Revolution General Commission, a network of activists across the country, said the checkpoint was "the last regime position" in the area in the south of Idlib province.

Khan Sheikhun "is now completely liberated," said the Observatory.

While rebels have been losing ground in the centre of Syria, they have in recent weeks been making steady progress in Idlib and north of neighbouring Hama province.

The Britain-based Observatory says opposition fighters have blocked access to the highway linking the south of Idlib province to rebel-held Morek in Hama province.

According to the Observatory, this latest advance brings rebels closer to taking over the Wadi Deif and Hamidiyeh army bases in the area, which opposition fighters have been besieging for over a year.

Also on Monday, three people were killed in an aerial barrel bomb attack in the Aleppo district of Bustan al-Qasr, as the regime kept up its bid to reclaim opposition-held areas of Syria's second city, said the Observatory.