Syrian troops and their allies, backed by Russian jets, attacked rebel-held towns north of the city of Homs on Thursday, targeting a long-held and strategic enclave of opposition to President Bashar al-Assad. The offensive that began before dawn builds on over a week of ground attacks launched with Russian air support in areas of western Syria that are crucial to Assad's survival and held by rebel groups other than Islamic State. Syrian state television, quoting a military source, said the army had begun a military operation in the area after heavy air strikes and artillery barrages early on Thursday. The Syrian Observatory for Human Rights, a UK-based group which monitors Syria's four-year-old civil war, said at least five civilians and six insurgents had been killed in Teir Malla, about 3 miles (5 km) north of Homs city. A resident said at least 25 people were killed including, Rawad al Aksah, a commander of insurgent group Liwaa al-Tawhid. A few miles further north, there were heavy air strikes around the town of Talbiseh and other villages in the area, the Observatory said, as well as fierce clashes on the southern edges of the town and nearby villages. Recapturing the area north of Homs would help reassert Assad's control over the main population centers of western Syria and secure territory linking Damascus to the coastal heartland of his minority Alawite sect. "The regime is actually getting its forces ready in all Homs's northern countryside ... What we fear is that they will follow the same strategy they had in Hama countryside. They actually attacked the fighters in all fronts at once," said local media activist Hassan Abou Nouh. The Syrian army, supported by foreign allies including Iran, has launched several ground offensives to retake insurgent-held territory since Russian jets started air strikes against rebel targets - mainly in western Syria - two weeks ago. The army operations include a campaign to recapture rebel-held land in Hama, Idlib and Latakia provinces in the northwest. Regional officials have also said the army, backed by Iranian reinforcements, is preparing for a ground operation around the city of Aleppo, close to the Turkish border. The Syrian military source quoted by state television said the army and its allies had taken control of the villages of Khalidiya and Dar Kabira, between Homs and Teir Malla. The Observatory said the army had advanced in Khalidiya, but there was still heavy fighting there. "There are very heavy air strikes in Homs on the frontlines. There are civilian casualties. The aim is to apply military pressure, and the regime's intention is to storm the area," said the leader of one rebel group operating in the area. He said the number killed was not confirmed but gave the names of five documented dead including a girl and two women. A resident of Talbiseh said four civilians had been killed there and that a school was hit at around 6 a.m., before classes started.