The Syrian army threatened to take the last main rebel supply route in Aleppo city on Friday, residents and activists said, which would trap opposition forces and civilians inside.

Although there are smaller, more indirect routes into Aleppo, taking the road would significantly reduce the rebels' ability to resupply and it would also allow the army to surround areas of the city which fell to insurgents two years ago.

"The road is completely closed and the regime has erected barriers," said Muhammad Bidour, a 25-year-old activist opposed to President Bashar al-Assad. "Our comrades were there and had to take another very long road which takes hours." Bidour said clashes were ongoing in the villages of Sifat and Dowir al-Zeitoun, around five miles north of Aleppo.

The Britain-based Syrian Observatory for Human Rights, which tracks violence in the country, said the army was not yet in control of the main road but that clashes centered around Handarat, a northern Aleppo district, had blocked the route. "If the army can take and hold Handarat, then Aleppo will be under siege," Observatory head Rami Abdulrahman said by telephone.

IN-DEPTH

—Reuters