The UN Human Rights Council on Friday voted for a special investigation into possible war crimes in Aleppo, just as Russia extended for another day a unilateral ceasefire in the besieged city.

The proposal spearheaded by the UK, with western and Arab backing, called for the UN's Commission of Inquiry on Syria to investigate "in particular the Syrian authorities and their allies" for possible war crimes in eastern Aleppo and demanded forces "end immediately all bombardments and military flights over Aleppo city."

UN human rights chief Zeid Ra'ad al-Hussein said that while extremists in eastern Aleppo had also killed residents, government forces and its allies were responsible for most civilian casualties. Russia and Syria criticized the resolution, which passed by majority vote, albeit with seven no votes and 16 abstentions to the 24 in favor.

Some 500 civilians have been killed in Aleppo since Russia and Syria launched a renewed offensive in late September to retake control of the rebel-held eastern part of the city, where an estimated 250,000 are trapped and unable to meet basic health and food needs.

Rebels, including the former al-Qaeda linked the Fateh al-Sham Front, have also launched indiscriminate attacks on government-controlled western-Aleppo.

Russia is under international pressure to step back from the Aleppo offensive and on Friday extended a "humanitarian pause," which began on Thursday, to Saturday evening. Moscow announced on Tuesday the Russian and Syrian air forces would temporarily stop bombing Aleppo to allow civilians and armed rebels to leave the city.

Kremlin spokesman Dmitry Peskov said on Friday that whether Russia extends a halt to bombings further "depends on  the process of fighters leaving the city - which so far is sluggish, unfortunately."

Russia and Syria accuse extremists, including the Fateh al-Sham Front, of blocking civilians and rebels from leaving. 

The Syrian opposition and rebels have said the humanitarian pause provides no guarantees for their safety and they would not comply.

The UN said on Friday that security concerns had forced it to delay planned evacuations and aid shipments.

It was not clear whether the security concerns related to Russian and Syrian actions or those of rebels who have not agreed to a ceasefire.

cw/msh (AFP, dpa, AP)