Russia has been confronted with sharp accusations at the United Nations of killing dozens of children and other civilians in Syria, provoking an angry response from Moscow's UN ambassador.

The UN's Children's Fund, UNICEF, and monitoring groups reported on October 26 that air strikes by Syrian or Russian warplanes killed 35 people, including at least 22 children and six schoolteachers in rebel-held Idlib Province.

"This is a tragedy. It is an outrage. And if deliberate, it is a war crime," UNICEF director Anthony Lake said.

Lake said the school compound in the village of Haas was "repeatedly attacked," in what may have been the deadliest attack on a school since the Syrian civil war began more than five years ago.

A photograph circulated on social media showed a child's arm, seared off above the elbow, still clutching the strap of a dusty black rucksack.

"When will the world's revulsion at such barbarity be matched by insistence that this must stop?" Lake asked.

Russian UN Ambassador Vitaly Churkin, apparently taken aback by the charges, said: "It's horrible, horrible. I hope we were not involved."

Churkin said he was consulting with the Russian Defense Ministry to determine who was responsible.

The Russian Defense Ministry on October 27 issued a statement saying that neither Russian nor Syrian government aircraft had conducted any air strikes in the Aleppo area over the last nine days.

Aleppo's 'Apocalyptic Horror'

Later, in a tumultuous meeting of the UN Security Council on the siege of Aleppo, UN humanitarian chief Stephen O'Brien accused Russia and Syria of using starvation tactics and turning the city into a "kill zone."

Describing what he called an "apocalyptic horror" in the city, where 400 people have been killed in less than a month, O'Brien accused Syria and Russia of waging a deliberate campaign to "make life intolerable, make death likely."

O'Brien said leaflets dropped on rebel-held areas of Aleppo by Syrian and Russian aircraft made their intentions "chillingly clear."

"This is your last hope.... Save yourselves," the leaflets read, according to O'Brien. "If you do not leave these areas urgently you will be annihilated."

O'Brien said he was "incandescent with rage" over the UN council's failure to stop the suffering. "The buck stops with you," he told members of the powerful panel.

That provoked an angry response from Churkin, who said it was "outrageous" that the UN had refused to acknowledge the humanitarian cease-fire that Russia says it has unilaterally imposed in Aleppo in the last week to allow delivery of humanitarian aid.

Churkin, who said that "terrorist" groups in Aleppo had prevented the delivery of the aid, accused O'Brien of "arrogance" for making such strong accusations against Moscow.

"If we needed to be preached to, we would go to a church," said Churkin, who is chairing the UN council this month. "Please leave this kind of report to a novel that you might write one day."

U.S. Ambassador Samantha Power assailed Russia for the latest violence, saying Moscow never worked cooperatively with the UN during its supposed pauses in fighting to ensure the delivery of humanitarian relief.

"You don't get congratulations and credit for not committing war crimes for a day or a week," she said.

Power insisted the goal of the Russian and Syrian bombing campaign was to "make civilians relent and cry uncle," and again challenged Moscow's claim that it is only fighting terrorists.

"Does Russia believe that all of the children in eastern Aleppo are Al-Qaeda members?" she asked.

After being upbraided before the council by Churkin, the UN's O'Brien said he would not "retract, qualify, or disclaim any fact or part of my earlier statement."

Turning to address Moscow's ambassador directly, O'Brien said: "I am prompted to state the age-old truth: Don't shoot the messenger. Stand up for the beleaguered people of Syria and...stop the war now."

With reporting by AP, AFP, Reuters, and dpa