BEIRUT (Reuters) - The Syrian government has recently expelled three United Nations staff, a move which will harm attempts to deliver desperately needed relief around the country, aid sources told Reuters on Friday.
Damascus denies that it blocks aid. Syrian officials could not immediately be reached for comment on these cases.
The expulsions come at a sensitive time, with U.N. mediator Staffan de Mistura arriving on Saturday to discuss his proposed plan for Damascus to suspend its bombardment and shelling of the northern city of Aleppo for a six-week period.
"We are extremely concerned that two OCHA staff, doing essential work with opposition parties on the ground to secure access for the delivery of urgently needed humanitarian supplies, have been asked to leave the country without any reason given," Jens Laerke, spokesman for the U.N. Office for the Coordination of Humanitarian Affairs (OCHA), said.
An aid worker from another organization, who was not allowed to speak publicly on the matter, said a high level member of the U.N. Children's Fund UNICEF was also made "persona non grata."
"This would have a major impact on vital aid operations in Syria, especially in terms of our ability to carry out local level negotiations for the safe passage of aid delivery," OCHA's Laerke said.
Aid workers in Syria say Damascus has in the past used threats of expulsion as a way of muting criticism and discouraging attempts to break the sieges.
Laerke said the staff were "essential field officers" but not whether they had already left Syria or when they were asked to leave. The aid worker said they were all senior foreign staff, working in the cities of Aleppo and Homs and asked to leave in recent weeks.
"I don't think the government will give a reason why. They just say, 'you have one week to leave'," the source said.
The United Nations says at least 212,000 people remain besieged, mostly by the government but also by insurgents.
In 2012, a U.N. agency chief ended a posting in Damascus after clashing with Syrian officials over access for aid distribution.
Simon Ingram, UNICEF's Regional Chief of Communication in the Middle East and North Africa, said: "I can't comment. We are still trying to establish the facts."
More than 200,000 people have been killed in Syria's conflict, which began in March 2011 with popular protests against President Bashar al-Assad and spiraled into civil war.