Russia said on Friday that a draft U.N. resolution for a truce in the Syrian city of Aleppo was unacceptable, as Moscow faced growing international pressure to stop a devastating bombardment of the city backed by Russian air power.
Russia's Deputy Foreign Minister Gennady Gatilov said a draft put forward by France contained a number of unacceptable points and politicized the issue of humanitarian aid.
But Foreign Minister Sergei Lavrov said Russia would support an eye-catching proposal by U.N. Syria envoy Staffan de Mistura to escort militants out of Aleppo personally.
Russia was ready to call on the Syrian government to allow fighters from the Islamist Nusra Front to leave the city with their weapons, Lavrov said.
Lavrov was speaking a day after Syrian President Bashar al-Assad offered fighters and their families an amnesty to leave rebel-held eastern Aleppo under guarantee of safe passage to other parts of Syria held by the insurgents.
However, rebels have told Reuters they do not trust Assad, and have said they believe such an agreement would be aimed at purging Sunni Muslims from eastern Aleppo.
The offer follows two weeks of the heaviest bombardment of the 5-1/2-year civil war, which has killed hundreds of people trapped inside Aleppo's eastern sector and torpedoed a U.S.-backed peace initiative.
More than 250,000 people are believed to be trapped in eastern Aleppo, facing severe shortages of food and medicine.
The war has already killed hundreds of thousands, made half of Syrians homeless, dragged in global and regional powers and left swathes of the country in the hands of jihadists from Islamic State who have carried out attacks around the globe.
The United States and Russia are both fighting against Islamic State but are on opposite sides in the wider civil war, with Moscow fighting to protect Assad and Washington supporting rebels against him.
German Chancellor Angela Merkel urged Russia to use its influence with the Syrian government to end the bombardment of Aleppo, as her government opened the door to possible sanctions against Russia for its role in the conflict.
Merkel said there was no basis in international law for bombing hospitals and Moscow should use its influence with Assad to end the bombing of civilians.
"Russia has a lot of influence on Assad. We must end these atrocious crimes," Merkel told an audience of party members in Germany.
U.S. Secretary of State John Kerry said Russian and Syrian actions such as bombing hospitals in Syria cried out for a war crimes investigation.
"Last night, the (Syrian) regime attacked yet another hospital and 20 people were killed and 100 people were wounded. Russia, and the regime, owe the world more than an explanation about why they keep hitting hospitals and medical facilities and children and women," Kerry told reporters in Washington.
"These are acts that beg for an appropriate investigation of war crimes and those who commit these would and should be held accountable for these actions."
Russia and Syria accuse the United States of supporting terrorists by backing rebel groups. The Syrian and Russian governments say they target only militants.
The U.N. Security Council was expected to vote on Saturday on a draft resolution that calls for an immediate truce in Aleppo, a no-fly zone and access for humanitarian aid.
French Foreign Minister Jean-Marc Ayrault, speaking through an interpreter as he and Kerry spoke to reporters before they met at the State Department in Washington said:
"Tomorrow, will be a moment of truth - a moment of truth for all the members of the Security Council. Do you, yes or no, want a ceasefire in Aleppo? And the question is in particular for our Russian partners."
Russia is expected to use its power of veto.
The Syrian army and its allies clashed on Friday in the south of Aleppo with rebels seeking to oust Assad, part of a pro-government offensive to retake the city.
The fighting was concentrated in Sheikh Saeed, a rebel-held district of the city next to Ramousah, where the most intense battles earlier this summer took place, but there were conflicting accounts of whether the army made any gains.
Air strikes on rebel-held eastern Aleppo by the Syrian military and Russian jets remained significantly lighter than during the previous two weeks following an army announcement on Wednesday that it would lessen its bombardment.
"Today there's no bombardment on the neighborhoods in the city, until now. We don't know what will happen in an hour," said Ammar al-Selmo, head of the civil defense rescue organization in Aleppo.
A Syrian military source said the army had captured several important positions on Sheikh Saeed's hilltop, but rebels said later that those gains had been reversed and that insurgents still held the area.
Since the start of an offensive two weeks ago, following the collapse of a short ceasefire, the army and its allies have made some progress in northern and central districts of rebel-held eastern Aleppo.
However, to completely storm eastern Aleppo could take months and would involve the destruction of the city and great loss of life, de Mistura said on Thursday.