WASHINGTON/DUBAI — A draft US-Russia plan calls for a cessation of hostilities in Syria to begin on February 27, but excludes Islamic State (IS) and al-Qaeda-linked Nusra Front militants, two western diplomatic sources said on Monday.

The sources, who spoke on condition of anonymity, confirmed a report by the Al Jazeera television network, which also reported that the draft calls on Syrian parties to agree to the cessation of hostilities by midday on February 26. One of the sources said this was accurate, but the second was unable to confirm it.

Islamic State attacked the Syrian government’s main supply route from Damascus to the northern city of Aleppo on Monday, a day after the group targeted Damascus and Homs in some of the bloodiest car bomb attacks of the war.

The Syrian Observatory for Human Rights said fighting and air strikes continued unabated across the country, a day after US Secretary of State John Kerry and his Russian counterpart, Sergei Lavrov, reached a provisional agreement on terms of a cessation of hostilities that would not include Islamic State.

Islamic State said it had taken control of a number of villages along an important road which connects government-held areas of Aleppo with the cities further south. A Syrian military source confirmed the attack, but said it was repelled. “They tried to attack this road, they were repelled and suffered big losses. After their losses, they are seeking any propaganda operation.”

The government has been making gains against Islamic State to the east of Aleppo, while also mounting major offensives against insurgents to the north and south of the city.

Islamic State is also under pressure from the Kurdish-backed Syria Democratic Forces alliance in the northeast.

The observatory’s director, Rami Abdulrahman, said government forces had reclaimed one of four positions seized by Islamic State on the road, which it has cut in previous attacks.

“The regime has recovered one of four positions that IS took on the road,” he said.