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Syrian regime forces edged closer to an Islamic State group bastion in the northern province of Aleppo on Thursday, capturing a nearby town.

Backed by intense Russian airstrikes, fighters loyal to President Bashar al-Assad seized Aarran from IS extremists, according to the Syrian Observatory for Human Rights.

The town lies just 10 kilometres (six miles) south of the IS stronghold of al-Bab.

"Regime forces are combing the town. There are some light clashes, but it is under government control," said Observatory head Rami Abdel Rahman. "This is the closest the government has been to Al-Bab since 2012," he added.

Roughly 30 kilometres (25 miles) south of the Turkish border, al-Bab fell into rebel hands in July 2012, and IS fighters captured it in late 2013.

Government forces are trying to cut off IS territory in Aleppo province from the group's stronghold in Raqqa further east, Abdel Rahman said.

Raqqa is the de facto Syrian capital of IS's self-styled "caliphate", which straddles Syrian and Iraqi territory.

The Aleppo offensive is part of a series of ground operations across the country backed by Assad's ally Russia, which began air strikes in Syria on September 30. 

The Russian air force carried out several massacres on Tuesday, in which around 80 civilians and were killed and dozens injured in brutal air raids on rural Aleppo and rural Idlib, the Syrian Coalition said.

Many children and women were among the victims.

According to Abdel Rahman, at least 63 IS fighters have been killed in Russian raids in the Al-Bab region since Saturday.

More than 260,000 people have been killed in Syria's conflict, which broke out in March 2011 with anti-government protests that spiralled into a multi-sided civil war.