GENEVA (Reuters) - Russia has agreed to a 48-hour humanitarian ceasefire in the divided Syrian city of Aleppo to allow aid deliveries, but security guarantees are awaited from other parties on the ground, U.N. officials said on Thursday.

The United Nations has pushed for a weekly 48-hour pause in fighting in Aleppo to alleviate suffering for about 2 million people, but major powers back opposing sides in Syria’s five-year-old civil war, complicating its implementation.

“We have ... agreement now from the Russian Federation for the 48-hour pause, we’re waiting (for) it from the other actors on the ground. That has taken more time frankly than I thought was needed,” Jan Egeland, who chairs the U.N. humanitarian task force, told reporters.

Egeland’s boss, U.N. Special Envoy for Syria Staffan de Mistura, echoed his comments, saying Russia was on board but they were waiting for others parties to agree: “... we are ready, trucks are ready and they can leave any time we get that message.”

Russia is the main external supporter of the government of Syrian President Bashar al-Assad. Rebel groups opposing Assad are supported by Western and Gulf powers.

The White House on Thursday said it supported U.N. efforts to bring all sides together to deliver humanitarian relief to Aleppo and would welcome Russia’s constructive engagement.

The U.S. State Department said while Washington backed the 48-hour Aleppo cease-fire it was focused on achieving a broader country-wide cessation of hostilities, which would be the focus of talks in Geneva on Friday.

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“If the U.N. says they need 48 hours, of course we support the U.N. But ... our focus is on a nationwide sustainable cessation of hostilities,” said State Department spokeswoman Elizabeth Trudeau. She said that would let all Syrians have access to aid and provide a basis for a political transition.

On Aug. 19, the main umbrella group for the Syrian opposition cautiously welcomed a proposal for a weekly truce in Aleppo, provided this would be monitored by the United Nations.

De Mistura has been trying to bring government and opposition representatives back to the negotiating table this month to revive a shattered broader ceasefire.

He said he awaited Friday’s meeting between U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov in Geneva before commenting further on his “political initiatives” to relaunch the political process.

The U.N. relief plan for Aleppo entails simultaneous deliveries of food to the rebel-held east and government-controlled west, Egeland said.

“First, a lifeline to eastern Aleppo, going cross-border from Turkey. Initially we would be ready in the first 48-hour weekly pause to have two convoys, of 20 trucks each, that would carry enough food for 80,000 people in eastern Aleppo,” he said.

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Western Aleppo, where needs have “increased dramatically”, would be supplied via Damascus, he said.

There would also be repairs of the electrical system in the “disputed south” that powers water pumping stations serving 1.8 million people.

Civilians in other encircled towns were also malnourished, Egeland said, singling out rebel-besieged Foua and Kefraya in Idlib and government-besieged Madaya near Damascus, which have not had U.N. food deliveries in 116 days.

“Starvation is just around the corner,” he warned.