Residents inspect damage after an airstrike on the rebel held al-Fardous neighbourhood of Aleppo. (Reuters)

ISIS fighters were reported to have tightened their grip on a Syrian government supply route to Aleppo on Tuesday as the army battled to retake the road as part of its campaign to seize the city.

As Damascus accepted a U.S.-Russian plan for a “cessation of hostilities” between the government and rebels due to take effect on Saturday, heavy Russian air strikes were also said to be targeting one of the last roads into opposition-held parts of Aleppo.

The plan announced by the United States and Russia on Monday is the result of intensive diplomacy to end the five-year-long war. But rebels say the exclusion of ISIS and the al-Qaeda-linked Nusra Front will give the government a pretext to keep attacking them because its fighters are widely spread in opposition-held areas.

The Syrian government, backed by Russian air strikes since September, said it would coordinate with Russia to define which groups and areas would be included in what it called a “halt to combat operations”. Damascus also warned that continued foreign support for the rebels could wreck the agreement.

The Russian intervention has turned the momentum President Bashar al-Assad’s way in a conflict that has splintered Syria and mostly reduced his control to the big cities of the west and the coast.

Damascus, backed by ground forces including Lebanon’s Hezbollah and Iranian Revolutionary Guards, is making significant advances, including near the city of Aleppo which is split between rebel- and government-control.

The ISIS assault has targeted a desert road which the government has been forced to use to reach Aleppo because insurgents still control the main highway further west.

The Syrian Observatory for Human Rights, which reports the war using a network of sources on the ground, said ISIS fighters had seized the village of Khanaser on the road, which remained closed for a second day. A Syrian military source told Reuters army operations were continuing to repel the attack.

ISIS, which controls swathes of eastern and central Syria, differs from rebels fighting Assad in western Syria because its priority is expanding its own “caliphate” rather than reforming Syria through Assad’s removal from power.

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