Syrian government forces have gained ground in a new push north of the divided city of Aleppo, seeking to cut a vital rebel supply line, a monitoring group said Tuesday.

The Syrian Observatory for Human Rights said regime forces had taken the villages of Bashkawi and Sefat and were battling to block the key highway leading from rebel-held east Aleppo to the Turkish border.

The fighting stopped traffic on the road, which passes through the town of Tal Rifat and up to the border.

The Britain-based monitor said fierce clashes were also raging between rebel forces and government troops in the nearby villages of Ratyan and Hardtaneen.

It said regime fighters were shelling the town of Hayan, which lies on the road to two government-held Shiite villages that rebels have besieged for more than 18 months.

"The regime troops have two goals in the area: to cut the road leading from Aleppo to the Turkish border, which is the key supply road for the rebels and to open the way to (besieged) Nubol and Zahraa," Observatory director Rami Abdel Rahman said.

Once Syria's industrial powerhouse, Aleppo city has been divided between rebel control in the east and regime control in the west since shortly after fighting there began in mid-2012.

In the surrounding countryside the situation is largely the reverse, with rebels controlling much of the area west of the city and regime forces much of the eastern countryside.

Government forces advanced around the east of the city last year, but the frontlines had been relatively static in recent weeks.

On Monday, Syrian daily Al-Watan, which is close to the government, said regime forces planned to encircle the city in a new offensive.

And the Observatory had reported an influx of troops reinforcing government forces in the area.

Inside Aleppo meanwhile, new fighting broke out on several fronts between government forces and rebels, the Observatory said.

It said at least six rebels had been killed in Rashideen district, and reported clashes in the Zahra and Old Aleppo districts.

Syrian state media gave no details on the new fighting, but reported that five people had been killed in rebel fire on districts in the government-controlled portion of Aleppo city.