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GENEVA (Reuters) - The United Nations Special Envoy for Syria called for all warring sides to agree by Sunday to allow the first safe delivery of relief supplies to the divided city of Aleppo.

The U.N. is seeking a weekly 48-hour humanitarian pause to deliver food, medicines and other aid to people in rebel-held eastern Aleppo as well as those in the government-controlled western part of Syria’s second city. It also wants to repair the electricity system to deliver power and clean water supplies to 1.8 million people, amid fears of disease outbreaks.

Staffan de Mistura said in a statement on Saturday that for logistical and operational reasons convoys must go via the Castello Road during the first pause, although he was aware of rebel opposition to using that government-controlled route.

“The Special Envoy calls for all concerned to exert every effort so that, by this Sunday, 28 August 2016, we know where we stand,” de Mistura said. There should be “no (military) escalation in areas adjacent or around the area of the pause”.

Russia, the main ally of the government of Bashar al-Assad, has already accepted the U.N. plan saying it is ready to ensure compliance, while the United States and other states are working to get other parties to commit, de Mistura said.

U.N. agencies have said that supplies including surgical material for treating war wounds and even baby milk have been removed from U.N. convoys at government checkpoints throughout the five-year conflict.

The main alliance of rebel groups in Aleppo, in a statement, gave conditional approval to use of Castello road but said the “shortest and fastest” Ramouseh road south of Aleppo should be used in parallel to deliver supplies to eastern Aleppo.

The United States and Russia failed on Friday to reach a breakthrough deal on military cooperation and a nationwide cessation of hostilities in Syria, saying they still have issues to resolve before an agreement could be announced.

De Mistura took part in those Geneva talks between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov.