By Jack Stubbs and John Davison

MOSCOW/BEIRUT (Reuters) – Russia said on Friday a draft U.N. resolution demanding an end to air strikes and military flights over 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 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.

“ATROCIOUS CRIMES”

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 said the call for an investigation was an attempt to distract from the failure of a U.S.-Russia brokered ceasefire, according to Tass news agency.

“It is very dangerous to play with such words because war crimes also weigh on the shoulders of American officials,” said Russian Foreign Ministry spokeswoman Maria Zakharova, according to RIA news agency.

Russia and Syria accuse the United States of supporting terrorists by backing rebel groups. The Syrian and Russian governments say they target only militants.

Russia has built up its forces in Syria since the ceasefire collapsed, sending in troops, planes and advanced missile systems, a Reuters analysis of publicly available tracking data shows.

The U.N. Security Council was expected to vote on Saturday on a draft resolution that calls for an immediate truce throughout Syria and access for humanitarian aid. It also “demands that all parties immediately end all aerial bombardments of and military flights over Aleppo city.”

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. Russian Deputy Foreign Minister Sergei Ryabkov told Interfax news agency Moscow had hoped talks with Ayrault, who was in Moscow earlier this week, “would help to find a way forward”.

“Instead of that, in New York we now have an attempt at political blackmail by putting to the vote, possibly tomorrow, a French resolution on the Syria crisis which is unacceptable for us.”

ALEPPO FIGHTING

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 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 those gains had been reversed and that insurgents still held the area.

Later in the day a number of air strikes hit areas of Sheikh Saeed, the Syrian Observatory for Human Rights monitoring group reported. Syrian state TV meanwhile reported that rebel shelling of government-held neighborhoods killed four people and wounded many more. The Observatory said insurgent shelling had killed 15 people in Aleppo over the past 24 hours.

The Observatory said that according to its own tallies, thousands of people had been killed in Russian air strikes over the past year, a significant number of them civilians.

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.

(Additonal reporting by Arshad Mohammed in Washington, Michelle Nichols at the United Nations and Angus McDowall in Beirut; Writing by Giles Elgood; Editing by Bernard Orr and James Dalgleish)