Diplomats, meeting in Paris for talks on the situation in Syria, have called for an immediate end to the violence in Aleppo and renewed talks with opposition leaders, even as air strikes continue to hit civilian areas in the city's east.
John Kerry, the US secretary of state and European foreign ministers, as well as their counterparts from Qatar and Saudi Arabia, also demanded on Saturday that Syrian government and Russian forces stop their onslaught.
For his part, Kerry said the Syrian government's "indiscriminate bombing" of eastern Aleppo amounts to "war crimes" and "crimes against humanity".
Kerry said "the indiscriminate bombing by the regime violates rules of law, or in many cases, crimes against humanity, and war crimes".
He urged Russia to show "a little grace" when US and Russian officials meet in Geneva, Switzerland, later on Saturday and pressed for a deal enabling civilians and fighters to leave besieged east Aleppo.
"Russia and Assad have a moment where they are in a dominant position to show a little grace," Kerry said.
"Fighters ... don't trust that if they agreed to leave to try to save Aleppo, that it will save Aleppo and they will be unharmed and free to move where they are not immediately attacked."
Mohammed bin Abdulrahman Al Thani, Qatar's foreign minister, accused the Syrian government of "genocide" and urged the international community to remain focused on finding a political solution to the conflict.
"Military confrontation does not offer a solution; there can only be a political solution," he said.
Speaking after the meeting, Jean-Marc Ayrault, France's foreign minister, said the Syrian opposition was willing to resume negotiations with Bashar al-Assad's government "without preconditions".
However, both Syria and Russia have rejected talk of a ceasefire without a withdrawal by fighters from the city, a demand that Syrian opposition groups have refused.
Al Jazeera's Imtiaz Tyab, reporting from Gaziantep on the Turkish side of the Turkey-Syria border, said the meeting offered little reprieve for civilians still trapped in east Aleppo.
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"Air strikes from Russian and Syrian jets have been relentless, as Syrian forces backed by Iranian militias engage in fierce street battles with rebels," he said.
"Residents have told Al Jazeera that the situation is a 'living nightmare' and while it is very hard to get a civilian death count, since Friday afternoon at least 56 civilians have been killed and several more injured."
Prospects look increasingly grim for the Western-backed opposition forces after five years of civil war, as forces loyal to Assad, backed by Russia and Iran, have captured about 85 percent of Aleppo's east, with fighters and civilians confined to just a few neighbourhoods.
The UN estimates about 100,000 people are now squeezed into opposition-held parts of Aleppo with virtually no access to food, water or medical care.
After days of intense bombing, Samantha Power, US ambassador to the UN, acknowledged this week that diplomacy has "not delivered for the people of Aleppo".
"We have engaged in that exercise in good faith for many, many months. But all that has happened in that period is that no food has arrived. No medical evacuations have occurred from eastern Aleppo. And the regime backed by Russia has pulverised schools, hospitals, civilian neighbourhoods," she told the Associated Press news agency.
Aleppo's loss would be the biggest blow for the opposition fighters in the conflict, which has killed more than 400,000 people and displaced half the country's population.
Blocked from leaving
Tens of thousands of civilians have fled east Aleppo in recent weeks, though the UN said on Friday it had received reports that the fighters had blocked some residents from leaving.
The Syrian Observatory for Human Rights (SOHR) says about 2,000 civilians fled east Aleppo on Saturday.
The state news agency, SANA, says they have been taken to a temporary shelter in Jibrin, about 10km east of Aleppo.
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The UN said on Friday it had received reports of fighters blocking some from leaving and of reprisals against residents who asked armed groups to leave.
It has also expressed concern about reports that hundreds of men had gone missing after fleeing to government-held territory.
The Syrian civil war started as a largely peaceful uprising against Assad in March 2011, but quickly developed into a full-scale war.
Source: Al Jazeera and news agencies