BEIRUT: The UN’s Syria envoy said Damascus is willing to facilitate a humanitarian cease-fire by halting fire on Aleppo, where regime troops are engaged in a new offensive to encircle embattled fighters.

The comments by Staffan De Mistura on Tuesday, came as regime forces severed the main fighter supply line into Aleppo in fighting that killed more than 150 people.

As clashes raged in the area, De Mistura announced that Damascus was willing to suspend its aerial bombardment of Aleppo city for a period of six weeks.

“The government of Syria has indicated to me its willingness to halt all aerial bombing and artillery shelling for a period of six weeks all over the city of Aleppo from a date we’ll announce from Damascus,” De Mistura told journalists after addressing the UN Security Council.

Fighters who hold parts of Aleppo but have no air power would be asked to suspend rocket and mortar fire for six weeks.

“The purpose is to spare as many civilians as possible while we try to find a political solution,” the diplomat said.

The announcement was the first sign of progress for De Mistura, who was appointed UN peace envoy for Syria in July.

Last year he proposed a plan to “freeze” fighting in Aleppo in a bid to allow humanitarian access, but the proposal failed to gain much traction.

And De Mistura incurred the wrath of the opposition last week by describing Bashar Assad as “part of the solution” to the country’s conflict.

On the ground, meanwhile, Syrian troops severed the main fighters’ supply route into the eastern half of Aleppo city, which is under opposition control, the Syrian Observatory for Human Rights said.

The highway runs up to the Turkish border through the town of Tal Rifaat, but regime forces now control two villages that straddle the route, effectively closing it to fighter traffic.

Aleppo city has been divided between regime control in the west and fighter control in the east since shortly after fighting began there in mid-2012. In the surrounding countryside the situation is largely the reverse, with fighters controlling much of the area west of the city and regime forces much of the east.

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

The severing of the highway leaves the rebels with only a long detour through the countryside available to them for resupply.