Fierce fighting raged Saturday between regime forces backed by Russian air strikes and Islamic State group fighters in northern Aleppo province, a monitor said.
The Syrian Observatory for Human Rights said at least 16 IS fighters had been killed in a failed attack on a regime position near the town of Al-Bab in the northeast of the province.
State television also reported that regime forces had repelled an assault.
Heavy fighting was ongoing on Saturday, the monitor said, with Russian war planes carrying out strikes in the region between the regime-held Kweyris air base and Al-Bab.
The regime has advanced towards the town, an IS bastion, in recent days, and is now within 10 kilometres (six miles) of it, according to the Observatory.
That is the closest regime forces have come to the town since 2012.
The Britain-based monitor also said regime forces had taken a string of villages nearby.
Roughly 30 kilometres (25 miles) south of the Turkish border, Al-Bab fell into rebel hands in July 2012, and IS jihadists captured it in late 2013.
The fighting in Al-Bab is just one of up to seven fronts on which regime forces are seeking to advance in Aleppo province, capitalising on a Russian air campaign that began on September 30.
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The various battles are intended in part to cut rebel supply lines into Aleppo city, the provincial capital and Syria's second city.
The city itself is divided and regime forces are now hoping to effectively encircle the opposition-held east.
"Through its operations, the army is trying to broaden its security zone around the city," and prevent rebels inside from receiving supplies and reinforcements from the suburbs, a security source told AFP this week.
A commander with pro-government forces said the regime was fighting on seven fronts across Aleppo province, including west and south of Aleppo city, and near Al-Bab.
In addition to cutting rebel access to eastern Aleppo city, the regime is hoping to sever areas controlled by IS in the province from its territory in neighbouring Raqa, Observatory director Rami Abdel Rahman said.
"If regime forces are able to reach the road that leads from Al-Bab to Aleppo, they will be able to tighten the noose around the fighters and the civilians that transport oil from areas under IS control."
Regime forces have launched offensives in several parts of Syria since the Russian campaign began.
After a slow start, the operations have scored some successes, including the recapture of the rebel stronghold of Salma in coastal Latakia province.
Elsewhere on Saturday, the Observatory said IS fighters had launched a multi-front attack against regime positions in the eastern city of Deir Ezzor with dozens reported dead.