Syrian rebels killed 28 soldiers in attacks on three army checkpoints on the main road from Damascus to the embattled city of Aleppo Thursday, a watchdog said.

Five rebels were also killed in the attacks near the city of Saraqeb in Syria's northwest, the Britain-based Syrian Observatory for Human Rights said.

The rebels did not capture the checkpoints, where they would be exposed to regime air strikes, but did seize several armoured vehicles, said the Observatory.

Syria's northwestern Idlib province has become a key battleground in the country's conflict, especially after rebel forces seized the town of Maaret al-Numan on the Damascus-Aleppo road early last month.

Fighting has since raged at the Wadi Deif army base near Maaret al-Numan, where rebel forces have laid siege to regime troops.