New York– The United Nations Security Council convened on Wednesday in an emergency session to discuss the deteriorating situation in the Syrian city of Aleppo.

The U.N. Envoy to Syria, Staffan de Mistura, called on the warring parties to allow the unconditional delivery of humanitarian aid to Aleppo, saying the fall of the eastern part of the city would lead to an unprecedented humanitarian crisis.

U.N. Humanitarian Chief Stephen O’Brien warned that eastern Aleppo was being turned into “one giant graveyard”, as the Syrian regime and Russian forces were overrunning the rebel-held area.

Since Saturday, 25,000 people had been forced from their homes in eastern Aleppo, more than half of them children, he said.

O’Brien added that those trying to flee the fighting faced new dangers, as rebel factions sought to stop them from leaving, or they were caught in the crossfire and then faced being seized and “disappeared” at regime checkpoints.

“For the sake of humanity, we call on, we plead, with the parties, and those with influence, to do everything in their power to protect civilians and enable access to the besieged part of eastern Aleppo before it becomes one giant graveyard,” O’Brien said.

Ambassadors of the United States, Britain and France lashed out at Russia and the Syrian regime for the ongoing airstrikes against the besieged city.

U.S. Ambassador Samantha Power accused Russia and Syria of pursuing a military solution at the cost of vast devastation to the city and its civilians.

She said the international community would resort to the U.N. General Assembly should Russia use its veto power again.

The French envoy, François Delattre, said the crushing of eastern Aleppo was not just a humanitarian calamity but also a strategic mistake.

The Russian ambassador to the U.N., Vitaly Churkin, said the Council should discuss the situation in the Middle East and North Africa as a whole, adding that millions of people were suffering from foreign interference.

Churkin strongly criticized De Mistura for failing to launch peaceful negotiations, and for disregarding the fact that the Syrian opposition factions have hampered peace efforts.

The U.N. envoy briefed the Council with updates on the situation on the ground, and his meeting with Syrian Foreign Affairs Minister Walid Al-Muallem last week on the “Aleppo Plan”, which calls for the immediate end to the bombardment of eastern Aleppo and the withdrawal of Nusra fighters from the city, while the area remains under the opposition’s administrative control.

De Mistura said that the Syrian regime has strongly rejected the plan despite the international envoy’s reassurances that the opposition would not impose self-governance, but would only form a local administration under the regime.