Daesh (so called IS) fighters seized the Syrian town of Maheen in Homs province from government forces on Sunday, a monitoring group said, expanding their presence in Syria's west despite a Russian-backed bombing campaign against them. Daesh's strongholds in Syria are in the north and east, but it has increased its territory in Homs province since taking over the historic city of Palmyra earlier this year, and then Qaryatain, 15 kms east of Maheen. The group began its attack late on Saturday using two suicide car bombs and by Sunday morning had taken over Maheen, the Britain-based Syrian Observatory for Human Rights said. The assault brought Daesh to within 20 kms (13 miles) of the main highway that links Damascus to Homs and to cities further north. The Observatory said at least 50 fighters on the government side were killed or wounded, and that clashes were raging further west on the outskirts of Sadad, a nearby town mostly inhabited by Christians, as Daesh pressed its advance. A statement from Daesh confirmed the assault on Maheen, describing the town as "strategically important" and saying it had also seized weapons caches. Russia and the Syrian government have been waging an air offensive against insurgents in the west and northwest of Syria. The Observatory's Rami Abdulrahman said the attack might have been a response to pressures the group is under elsewhere. "Daesh always looks for advances against the regime after failures in the areas it controls in northern Syria," he said, without referring to specific battles in the north. Government and Russian airstrikes have been targeting Daesh fighters at an airbase they have long besieged in Aleppo province. Fighting there has drawn support from Damascus ally Iran and killed an Iranian general several weeks ago. . Daesh is also under pressure in the northeast province of Hasaka, after a new US-backed rebel alliance launched an offensive against the group near the Iraqi border. Meanwhile, UN peace envoy Staffan de Mistura met with Syrian Foreign Minister Walid Muallem on Sunday in Damascus, two days after attending international talks on Syria's four-year war, a UN official said. The Syrian newspaper Al-Watan, which is close to the government, said the UN envoy was in Damascus to brief officials on the "details" of the Vienna talks. Top diplomats from 17 countries, as well as the United Nations and the European Union, gathered on Friday in Vienna to narrow their divisions over the war, which has killed more than 250,000 people. De Mistura was expected to leave Damascus on Monday, the UN official said, declining to provide further details on the diplomat's visit. Syria's state television said Muallem had "expressed to... de Mistura the importance of numerous points" in the statement released at the end of the Vienna talks.