GENEVA: A United Nations humanitarian task force has been unable to make deliveries to desperate Syrians for the past two months as President Bashar Al Assad’s government has withheld approval for aid convoys, the UN humanitarian adviser said on Thursday.

Before they can move into besieged areas or across front lines, the convoys require letters from the government and security guarantees from armed groups.

“It’s an all-time low in giving us the facilitation letters,” adviser Jan Egeland told reporters after meeting senior diplomats in Geneva.

Insurgents fighting Assad’s forces were also creating obstacles, contributing to the worst situation since 2015, he said.

Egeland called on Russia, Turkey and Iran to de-escalate the fighting in Idlib governorate, which he said was “screaming for a ceasefire.”

“When we need their ability to influence the parties the most, in this bleak hour for humanitarian work, humanitarian diplomacy seems to be totally impotent. We’re getting nowhere at the moment.”

This week Russia convened a Syrian peace congress in Sochi. Egeland said it had so far not resulted in any progress but he hoped that it would.

Air strikes hit two crowded markets in Idlib this week, killing at least 31 people, and have deprived hundreds of thousands of healthcare.

“I told the members of the humanitarian task force, we cannot have conventional warfare in what is essentially a refugee camp,” Egeland said.

Further north, a Turkish offensive in Afrin district has displaced about 15,000 people, Egeland said, adding: “There are also reports...that local authorities have made it hard for people to flee from the Afrin area.”

And outside Damascus, the rebel-held enclave of Eastern Ghouta, where almost 400,000 people are under siege and about 750 need urgent medical evacuation, desperately needs a pause in the fighting, he said.

“We have indications from both sides that they want it, but it hasn’t happened. And it’s both sides that have to help us here. There are air raids, fighting from the government side, but there is a barrage of mortars and grenades going from this area going into civilian neighbourhoods in Damascus.”

He also said 112 people had been killed by explosions in the town of Raqa since it was recaptured from Daesh fighters in October because people had been allowed back to their homes before the town had been cleared of bombs.

Meanwhile, the Syrian government described a Turkish offensive in Syria’s Afrin region as an illegal “aggression” and said it would deal with it accordingly.

“The Turkish military operation in northern Syria is a blatant aggression,” said a foreign ministry statement circulated on state media. The unauthorised presence of foreign forces represents “occupation and will be dealt with on this basis,” it said.

The chief opposition negotiator said on Thursday that Syria’s opposition will cooperate with proposals made at a Russia-hosted conference this week to rewrite the country’s constitution as long as the process remains under UN auspices.

Participants at Tuesday’s meeting in the Black Sea resort of Sochi in Russia — which is a powerful supporter of Assad — agreed to set up a committee to change the Syrian constitution, and called for democratic elections.

The main Syrian negotiating group had boycotted the gathering, while the United States, Britain and France also stayed away because of what they said was the Syrian government’s refusal to properly engage.

However, chief opposition negotiator Nasr Hariri said the Syrian Negotiation Commission would “work positively” with the proposed committee because responsibility for setting it up had been handed to UN Syria envoy, Staffan de Mistura.