Heavy fighting is raging around the city of Idlib in northwestern Syria as rebels press their offensive against the government stronghold.

An array of armed opposition groups began their operation this week against Idlib, the provincial capital and home to some 165,000 people. Rebels have long controlled most of the surrounding towns and countryside, but President Bashar Assad's forces have maintained their hold on the city.

The Britain-based Syrian Observatory for Human Rights said Thursday the rebels have seized at least 17 checkpoints and military outposts from pro-Assad troops. It said at least 11 government fighters and 17 rebels have been killed.

Late Wednesday, Syria's state news agency said the army killed "tens of terrorists" on the eastern side of Idlib. The government refers to Assad's opponents as "terrorists."