The UN's World Food Programme raised alarm on Tuesday that escalating violence in Syria could derail a fragile truce that has helped facilitate increased aid deliveries.

In an interview with AFP in Damascus, the WFP's deputy regional head Matthew Hollingworth said the UN and aid agencies hoped the truce -- which came into force on February 27 -- could hold.

"The ceasefire has been so important over the last weeks because it has given people a lot more than simply access to markets, access to assistance. It has given them hope," Hollingworth said.

"The end of the ceasefire would dash that hope," he said.

The truce between the regime and non-jihadist rebels has seen fighting drop in northern and central Syria, allowing UN agencies to deliver desperately needed aid.

About 4.5 million people are living in besieged or hard-to-reach areas in Syria, according to the UN.

In March, the UN was able to deliver aid to 83,000 people in hard-to-reach areas -- up from 53,000 in February.

"They are really at the end of their tether. The difficulties that they are facing are enormous," Hollingworth said.

"If the ceasefire does end, then clearly we will have to find other ways to have access to people. But it's going to be harder and harder to negotiate" access, he added.

The truce does not cover the fight against jihadists of the Islamic State (IS) group and the Al-Qaeda-affiliated Al-Nusra Front.

IS extremists have surrounded the eastern city of Deir Ezzor, where more than 200,000 people -- mostly women and children -- still live.

On Tuesday, the WFP announced it had dropped 26 food pallets to Deir Ezzor's besieged residents in its second successful airdrop on the city in several days.

Hollingworth said the second air delivery brought the total number of people supported by WFP aid drops over Deir Ezzor to 4,500.

The WFP said on Sunday it had carried out its first ever successful high-altitude airdrop, to deliver 20 tonnes of food aid to the city.

"There are very limited opportunities to use air dropping at high altitudes around Syria," Hollingworth said.

He said the German, Russian, Italian, Dutch and American governments were all supporting the air operations.

"We are dropping anything between 16 tonnes to 22 tonnes each time we make the airdrops," he added.

"We hope that in doing so we can cover more than 100,000 people per month, not only with just food, with food assistance, nutrition assistance, water and sanitation, as well as medical and health care."

The airdrops are "the very last resort" in terms of aid delivery methods and are the first of its kind in the UN's history, Hollingworth said.

UN aid agencies typically deliver food and medical assistance through convoys of aid trucks after negotiating with parties to Syria's conflict for safe passage.

More than 270,000 people have been killed since Syria's conflict erupted in 2011, and millions have fled their homes.

Source: AFP