The US ambassador to the UN has lashed out at the Syrian government, and its allies Russia and Iran, saying they bear the responsibility for the "carnage" in Aleppo.

Speaking during an emergency UN Security Council meeting, Samantha Power used strong language as she addressed her counterparts directly.

"To the Assad regime, Russia and Iran, three member states behind the conquest of and carnage in Aleppo: you bear responsibility for these atrocities," she said.

"Is there literally nothing that can shame you?

"Is there no act of barbarism against civilians, no execution of a child that gets under your skin?"


:: Aleppo under siege: A timeline

Image: Thousands of civilians fled Aleppo as government forces closed in

During PMQs in London, Theresa May also pointed to Russian President Vladimir Putin for the humanitarian disaster.

"Enough is enough in Aleppo. We need to ensure that humanitarian aid is there for people," the PM said.

"It's in President Putin's hands, he can do it - why doesn't he?"

The UN meeting was held as a ceasefire and evacuation agreement was brokered by Russia and Turkey to end years of fighting in the city and allow the evacuations of thousands of civilians and rebels.

However, the deal appeared to break down as fierce fighting, including gunfire and shelling, resumed on Wednesday. And the evacuation plan was put on hold.

Turkish President Tayyip Erdogan accused Syrian government forces of violating the truce, but said he would talk to Mr Putin in an effort to rescue the plan.

"The situation on the ground is very fragile and complicated," he said on Wednesday.

The Syrian forces have been making gains in the rebel-held eastern parts of the Aleppo for weeks, and were close to wrestle full control of what was once Syria's largest city.

Ban Ki Moon: 'It's past the time to act and force others to act'

UN secretary-general Ban Ki-moon told the emergency meeting he had received "credible reports" of civilians killed by intense bombing and summary executions by pro-government forces.

UN officials had said earlier that civilians were being shot "on the spot" and in their homes.

"It is your noose," Ms Power said.

"Three member states of the UN contributing to a noose around civilians. It should shame you. Instead, by all appearances, it is emboldening you. You are plotting your next assault. Are you truly incapable of shame?"

Image: A demonstration in London calling for the end of violence in Aleppo

In a tense climate, where insults often replaced diplomacy, the Russian ambassador said Ms Power was behaving "like Mother Theresa" and accused the US, UK and France of distributing fake news about the crisis.

Russia, Bashar al Assad's closest ally, has vetoed the last six UN resolutions aimed at easing the dire situation in Aleppo.

Syria's UN ambassador hailed "the liberation of Aleppo" from "terrorists" who controlled the east of the city.

UN: Aleppo civilians paying 'brutal price'

Bashar Jaafari told the meeting that he "firmly and 100%" rejected allegations that Syria has been committing "acts of revenge, summary executions and terror" against civilians.

France's UN ambassador Francois Delattre, whose country had requested the emergency meeting along with the US, said "war crimes and potentially crimes against humanity are committed on a daily basis in Aleppo."