The United Nations envoy to Syria expects a staggered start to peace talks next week, with participants arriving over several days for "indirect meetings", he said in an interview with pan-Arab newspaper Al Hayat.

"I see us beginning on March 10 when we will launch the process," Staffan de Mistura said. "Some (participants) will arrive on the 9th. Others, because of difficulties with hotel reservations, will arrive on the 11th. Others will arrive on the 14th."

The talks will be conducted indirectly rather than face-to-face.

"We will hold preparatory meetings and then go into detail with each group separately," he said.

Mr de Mistura attempted to convene peace talks in January, but these failed before they had even started in earnest.

The five-year Syrian civil war has killed more than a quarter of a million people and created a massive refugee crisis for Lebanon,Turkey and the European Union.

The new effort follows the implementation of a partial truce a week ago, though fighting continues in many parts of Syria as the truce does not include the so-called Islamic State and Nusra Front groups.

The reduction in violence has made aid deliveries easier in some areas of the country, but Mr de Mistura said the Syrian government should be processing aid faster.

"Lorries are waiting for 36 hours," he said. "And medical aid must be allowed."

On Wednesday, the World Health Organization said Syrian officials had rejected the delivery of medical supplies, including trauma and burn kits and antibiotics, in a convoy to the besieged town of Moadamiya two days earlier.

Mr de Mistura said he plans to invite members of the government, the opposition, civil society and women to the peace talks.

"Women are important to us because they have a lot to tell us about the future of Syria. We will meet with them separately," he said.

Meanwhile, a British-based monitoring group has said 135 people were killed in areas covered by the truce in its first week.

The Syrian Observatory for Human Rights, which follows the conflict through a network of sources on the ground, released the figures one week after the cessation came into effect.

They added that 552 people have been killed in areas not covered by the cessation.