UN Secretary General Ban Ki-Moon
UN Secretary General Ban Ki-MoonReuters

UN Secretary-General Ban Ki-moon said on Monday he is alarmed by reports of atrocities against "a large number" of civilians, including women and children, in recent hours in the Syrian city of Aleppo.

"While stressing that the United Nations is not able to independently verify these reports, the secretary-general is conveying his grave concern to the relevant parties," said Ban’s spokesman Stephane Dujarric, according to AFP.

Ban has asked his envoy Staffan de Mistura to follow up, according to the report.

"The United Nations underlines the obligation of all parties on the ground to protect civilians and abide by international humanitarian and human rights law," Dujarric said.

"This is particularly the responsibility of the Syrian government and its allies," notably Russia and Iran, he added.

Ban’s statement came after the Syrian army said its military operations to crush the remaining pockets of resistance from opposition fighters in Aleppo were entering the final phase after months of heavy fighting.

About 10,000 Syrians have fled rebel areas in the past 24 hours, mostly to government-held territory, according to the Syrian Observatory of Human Rights.

Last week, the United Nations reported that hundreds of men had gone missing after fleeing the battered city.

The fall of Aleppo would be the worst rebel defeat since Syria's conflict began in 2011, and leave the government in control of the country's five major cities.

During the fighting in Aleppo there were reports of hundreds of casualties, including one attack which killed at least eight schoolchildren.

That attack promoted de Mistura to warn that “time was running out” to avoid a humanitarian catastrophe in the city.

More than 300,000 people have been killed since the conflict began in March 2011, and over half the population has been displaced, with millions becoming refugees.

Moscow launched an air war in support of President Bashar Al-Assad's forces last year, while Washington has supported rebel forces battling the regime.

AFP contributed to this report.