Turkey called for a ceasefire to allow the evacuation of civilians. France pressed for an immediate UN Security Council resolution to discuss atrocities reportedly carried out by the Syrian regime and its allies.
Turkey, France, Britain and the United Nations on Tuesday responded to the civilian crisis in eastern Aleppo as Syrian regime forces and their allies closed in on the last neighbourhoods held by the opposition.
Rebel defences in Aleppo collapsed on Monday, forcing thousands of civilians to flee the frontlines of the battlefields across the remaining insurgent pocket in the city.
The UN said it had reports that 82 civilians, including 11 women and 13 children, were killed by pro-regime forces in recent days.
Turkey said it was "horrified and outraged" by the allegations of the massacre of civilians. Turkish Foreign Minister Mevlut Cavusoglu said a cease fire was needed to allow the evacuation of civilians.
"We're seeing the most cruel form of savagery in Aleppo, and the regime and its supporters are responsible for this," he told a news conference in Ankara.
A senior Turkish official said Turkey was negotiating with Russia to open a corridor to evacuate Syrian rebel fighters and civilians from the remaining opposition-held districts of Aleppo.
France called for an immediate UN Security Council resolution to discuss alleged atrocities being carried out in eastern Aleppo, Foreign Minister Jean-Marc Ayrault said.
"In the face of allegations of executions in Aleppo, France calls for a UN Security Council meeting," Ayrault said on his Twitter account.
United Nations Secretary-General Ban Ki-moon on Tuesday urged the Syrian regime and its allies, Russia and Iran, to "urgently allow the remaining civilians to escape" Aleppo and facilitate humanitarian aid access to the beseiged city.
Britain's House of Commons held an emergency debate on Aleppo.
UN human rights chief Zeid Ra'ad al Hussein called on the international community to demand Syria allow monitoring of its treatment of people fleeing eastern Aleppo, warning that populations of other rebel-held towns could face the same fate.
"The crushing of Aleppo, the immeasurably terrifying toll on its people, the bloodshed, the wanton slaughter of men, women and children, the destruction - and we are nowhere near the end of this cruel conflict," Zeid said in a statement.
Syrian regime leader Bashar al Assad's forces now hold almost all of the one-time opposition stronghold of east Aleppo, and appear on the verge of retaking the entire city.