BEIRUT: Heavy air strikes targeted areas of Hama province captured by Syrian insurgents from government forces in recent days, as Damascus counter-attacked on Thursday in an area of strategic importance to President Bashar al-Assad.

The Syrian Observatory for Human Rights said at least 17 people had been killed in the air strikes overnight. Syrian state TV said the air force had launched "concentrated strikes" against what it described as terrorists in the area, saying tens of them had been killed.

The rebel offensive launched on Tuesday threatens loyalist areas populated by Christians and Alawites just east of the coastal mountains that are the heartland of Assad's Alawite sect.

The rebel groups taking part include the jihadist Jund al-Aqsa and factions fighting under the banner of the Free Syrian Army (FSA). Jaish al-Nasr, one of the rebel groups, said in a statement released overnight that two commanders and three other of its fighters had been killed in the Hama battles.

The Observatory said the 17 people had been killed in air strikes targeting a road between the town of al-Latamenah and Idlib province, an area of northwestern Syria that is mostly under insurgent control.