U.N. aid convoys resumed on Thursday aid delivery to besieged areas in Syria after a 48-hour suspension to review security guarantees following a deadly attack on relief trucks and a warehouse near Aleppo, a U.N. spokesman said.

“Today we are sending an inter-agency, cross-line convoy with urgently needed aid to people in a besieged area of rural Damascus,” United Nations humanitarian agency (OCHA) spokesman Jens Laerke said in a statement.

“We have resumed aid deliveries based on the humanitarian imperative,” he added.

The Syrian Arab Red Crescent said the convoy attack killed a staff member and around 20 civilians.

U.S. officials believe Russian aircraft were responsible for the strike, but Moscow has denied involvement and the Russian Defense Ministry said on Wednesday a U.S. Predator drone was in the area when the convoy was attacked.

This was the first convoy to head towards a besieged area since Monday’s attack, Laerke told reported.

“It’s important to understand that the security situation in Syria is not one situation, it’s a patchwork of different levels of security or insecurity, it’s a patchwork of multiple actors and armed groups, and we need to take that into account when we evaluate on a case-by-case basis,” Laerke said.

“So that is what we do, whether we send it to rural Damascus as we do today, or hopefully in the near future we can resume deliveries in Aleppo and elsewhere in Syria,” he added.

The U.N. has estimated that roughly 600,000 people are stuck in Syria’s 18 besieged areas.

Accessing them and others in so-called hard-to-reach areas has become a top U.N. priority.

Convoys have repeatedly been blocked for security reasons, refusals by the Syrian regime to grant authorization and strict conditions imposed by opposition groups.

The U.N., Red Cross and other humanitarian agencies had hoped that a ceasefire agreed earlier this month would allow them to get life-saving supplies to more than a million Syrian civilians.

But the ceasefire’s collapse has held up aid deliveries.

The United Nations hopes countries backing the Syria peace process will agree on Thursday to salvage the ceasefire, enabling a return to peace talks within weeks, U.N. Deputy Special Envoy for Syria Ramzy Ezzeldin Ramzy said.

Ramzy said the United States and Russia had the backing of other states in the International Syria Support Group (ISSG), which is to meet for a second time this week in New York later in the day, to reinvigorate their joint plan for a truce.

“Clearly the resumption of the talks would be greatly helped by revitalizing the cessation of hostilities,” Ramzy told reporters in Geneva. “That is the objective of the meeting of the ISSG.”