Islamic State fighters took control of a section of road southeast of Aleppo on Friday, threatening the Syrian army's only supply route into the city, a group that monitors the civil war said.

Islamic State captured parts of a road running between the towns of Khanaser and Ithriya, said Rami Abdulrahman, head of the British-based Syrian Observatory for Human Rights. He said battles were continuing in the area.

Al Qaeda's Syria wing and other insurgents are also battling pro-government forces in surrounding areas, said Abdulrahman, who tracks the conflict using sources on the ground.

Islamic State said in a statement distributed online that it had taken control of eight army checkpoints on the road and cut off the army supply route to Aleppo, which was Syria's most populous city and commercial hub before the war broke out in 2011.

A report on Syrian state news agency SANA did not mention the road but said the army and local militia had taken control of four villages southwest of Aleppo on Friday.

Areas around Aleppo have seen days of heavy fighting after Syrian troops backed by Lebanese Hezbollah and Iranian fighters launched an offensive last week to retake territory around Aleppo from rebels and jihadist fighters.

The offensive has concentrated so far on clearing insurgent-held areas south of Aleppo rather than the city itself, which is home to 2 million people and divided between government forces to the west and rebels in the east.

The operation to retake areas around the northern city is one of several assaults carried out by pro-government ground forces since Russian jets began carrying out air strikes on Sept. 30 in support of President Bashar al-Assad.

Syrian troops are also trying to advance to the east of Aleppo towards Kweires military airport, aiming to break a siege of the base by Islamic State and other insurgents.

(Reporting by Sylvia Westall; Editing by Mark Trevelyan)