United Nations (United States) (AFP) - Pro-Russian rebels have ordered UN agencies working in the separatist stronghold of Lugansk in east Ukraine to leave the area by Friday, the UN aid chief said.

Several international non-governmental organizations have separately been told to leave Lugansk by Saturday, Stephen O'Brien said in a statement Thursday.

O'Brien said he was "alarmed" by the decision and called on the separatists "in both Lugansk and Donetsk to ensure the immediate resumption of UN and international NGO activities."

Pro-Russian leaders said earlier they had banned 10 Western relief groups including Doctors Without Borders (MSF) for "gave violations" of laws.

The Lugansk guerrillas have accused MSF of "illegally storing psychotropic medication" that lacked proper registration in either Russia or Ukraine. MSF strongly denies the allegations.

O'Brien, the UN under-secretary-general for humanitarian affairs and emergency relief coordinator, said some 16,000 tons of humanitarian aid had not been delivered and that local hospitals could not perform surgery because they lack anesthesia.

In an indirect appeal to Russia, O'Brien urged "everyone with influence over the de facto authorities to use that influence to ensure the immediate resumption of humanitarian aid by UN agencies and international NGOs."

The move came ahead of an October 2 meeting in Paris of Russian President Vladimir Putin with his Ukrainian counterpart Petro Poroshenko to try to advance peace prospects.

The United Nations estimates that the 17-month conflict in east Ukraine has claimed the lives of nearly 8,000 people and injured almost 18,000 -- most of them civilians.