GENEVA (Reuters) - U.N. Syria envoy Staffan de Mistura called on Russia and the United States on Thursday to work together in reducing the fighting in Syria, saying that failure of their cooperation plan would have a very negative impact on planned peace talks.
U.S. and Russian military officials were coming to Geneva to discuss details, he told reporters after a weekly meeting of the humanitarian task force.
"We are all awaiting and urging the two co-chairs - which means Russia and the U.S.- to expedite their own discussions on how to reduce violence," de Mistura said.
"I understand that there are several experts from the military establishment from both Russia and perhaps from the U.S. on their way to Geneva and probably, most likely, in order to discuss the so-called 'devil in the details' which are the ones we have been asking to be sorted out as soon as possible."
U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov have met in Moscow and Laos in recent weeks to try to hammer out a deal on military cooperation that is widely seen as a key to reinstating a nationwide ceasefire.
Russia and the United States are both conducting air strikes in Syria against Islamic State fighters, but support opposing sides in a wider civil war, with Moscow backing President Bashar al-Assad's government and Washington saying he must leave power.
Moscow and Washington jointly sponsored a ceasefire and peace talks earlier this year, but the truce largely collapsed in May and the talks have yet to resume amid the fighting, although de Mistura hopes to reconvene them in late August.
Meanwhile, Assad's forces have advanced in northern Syria, besieging the rebel-held section of the divided city of Aleppo, potentially the government's biggest prize of a 5-year-old civil war that has killed hundreds of thousands of people and displaced many millions.
Russian Defence Minister Sergei Shoigu said on Thursday the Russian and Syrian militaries would start a large-scale humanitarian operation in Aleppo during which civilians and militants would be given the chance to leave the besieged zone.
De Mistura said it would be premature to comment on Russia's aid proposal or Syria's suggestion of an amnesty for surrendering fighters in eastern Aleppo. He said the United Nations, "like everyone else", was not consulted on the proposals beforehand.
"The city is de facto besieged, because it is almost completely militarily encircled," he said, and there were only 2-3 weeks of supplies left. "The clock is therefore ticking, there is no doubt about that."
There are only 31 doctors and 3 dentists left in rebel-held eastern Aleppo, home to about 300,000 civilians, said Dr. Tawfik Chamaa, of the Union of Syrian Medical Relief Organisations (UOSSM).
Chamaa, referring to a proposed humanitarian corridor for civilians, told a briefing: "We would like this to be realized for sure, under international supervision....We don't know the intention of the Russian and Syrian forces."
Reporting by Stephanie Nebehay and Tom Miles; editing by Peter Graff