The U.N. political chief told an emergency meeting of the U.N. Security Council on Wednesday that the Syrian government's bombing campaign in Aleppo over the last two weeks is among "the worst" of the five-year war and he demanded that perpetrators be brought to justice at the International Criminal Court.

Jeffrey Feltman said he wanted to make clear that intentional and direct attacks on hospitals are war crimes and so is using starvation as a weapon during conflict.

Once Syria's largest city and commercial center, he said, Aleppo is being subjected to "systematic destruction" and is increasingly becoming "a shell of what it once was." He said "opposition shelling of government-controlled neighborhoods has also led to death and destruction."

Feltman and U.N. humanitarian chief Stephen O'Brien called for the cessation of hostilities in Aleppo — agreed to by the U.S. and Russia and announced Wednesday — to be implemented fully and immediately. That call was echoed by virtually all 15 council members who spoke at the meeting.

O'Brien said hundreds of civilians have been killed or injured in "the carnage in Aleppo" in the last 10 days and blamed all parties.

"Life for people in Aleppo is horrendous and has lost all sense," he said, pointing to the roughly 300,000 people in eastern Aleppo living in constant fear of aerial attacks and the estimated 1.3 million in the west crowding into basements to escape shelling and mortar rounds.

Syria's deputy U.N. ambassador Mounzer Mounzer told the council that "what the Syrian government has been doing in the city of Aleppo is merely a fulfillment of its obligation to protect its citizens from terrorism."

He said the Syrian government abided by the cessation of hostilities that went into effect in late February and accused armed groups allied with the Nusra Front, an affiliate of al-Qaida, of violating the agreement, particularly in Aleppo.

Russia's U.N. Ambassador Vitaly Churkin, a close Syrian ally, urged support for the Russian-American efforts and a peace agreement, and "an end to all provocations." Alluding to allegations that the Syrian government is responsible for widespread bombings and attacks, Churkin said, "it's counterproductive to express public criticism on unverified incidents simply to add new charges against the Syrian government."

British Ambassador Matthew Rycroft, who called for the emergency meeting on Aleppo, demanded to know how Syrian President Bashar Assad and his allies can say they are protecting their people and justify the encirclement and assault on Aleppo including the shelling of hospitals and schools.

"These attacks amount to nothing more than barbaric, collective punishment," Rycroft said. "They are war crimes ... (and) those responsible should be held fully accountable including at the International Criminal Court."