Turkey called on the United States and other nations Monday to rethink its proposal for a no-fly zone in northern Syria as the U.N. expressed deep concerns over the bombing of hospitals in rebel-held parts of Aleppo.

Government forces pounded besieged rebel-held neighborhoods of the northern city for a seventh day, raising fears for the civilian population after airstrikes hit most of the hospitals in the area over the weekend.

"There are no more working hospitals in eastern Aleppo, where more than 100,000 children are trapped under siege and heavy bombardment with dwindling access to food and medicine," said Geert Cappelaere, regional director for the U.N.'s children's agency. "They need these hospitals to stay alive."

"Children should not be dying in hospitals because of bombs and they should not be dying in schools," he said, referring to a school that was hit on the government side of the city on Sunday, killing eight students.

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Turkey has long called for a no-fly zone to protect Syrian opposition forces from President Bashar Assad's air force. Ankara sent its own ground troops into Syria in August, but they are not fighting the Syrian government. Instead, Turkish forces and allied Syrian opposition fighters are battling the Islamic State group and U.S.-backed Kurdish forces, which Ankara views as an extension of the Kurdish insurgency in southeastern Turkey.

Addressing a NATO parliamentary assembly in Istanbul, Turkish President Recep Tayyip Erdogan again criticized allies' reliance on Syrian Kurdish fighters to battle IS.

"I hope that in the upcoming process, this will be reassessed, especially by the United States, and positive steps will be taken so that terrorism's back is broken and Turkey is rid of the threat of terrorism," Erdogan said.

Turkey's positions have put it at odds with Washington, which has refused to directly target Assad's forces while providing air support for the Syrian Kurds, who have proven to be among the most successful ground forces battling IS.

It's unclear how those policies might change under President-elect Donald Trump, who has expressed skepticism about American support for Syrian rebels and hinted at joining forces with Moscow against IS.

Erdogan's comments came after Adnan Abu Amjad, a Syrian rebel commander allied with Kurdish forces, said Turkish warplanes struck his group near the northern town of Manbij late Sunday, killing one fighter and wounding others.

"The Turkish state is a terrorist state that is attacking positions of the military council that is fighting Daesh," said Abu Amjad, commander of the Manbij Military Council, using an Arabic acronym to refer to IS.

Russian warplanes are also soaring through Syria's crowded skies, striking insurgents in a massive offensive announced last week that is aimed at shoring up Assad's forces.

"The bombing that is conducted by the Russian and Syrian air forces is just adding to the human suffering in Syria," NATO Secretary General Jens Stoltenberg told the assembly in Istanbul.

He said Syrian government forces are responsible for "indiscriminate bombing" in Aleppo, Syria's largest city, which has emerged as the epicenter of the civil war.

The Local Coordination Committees, an activist monitoring group, said Monday's shelling of east Aleppo killed and wounded several people. The Britain-based Syrian Observatory for Human Rights said five people were killed in Monday's bombardment.

On Sunday, pro-government forces advanced into parts of the strategically important Hanano district, according to state media and the Observatory.

The Observatory and the LCC also reported bombardment of several suburbs of the capital Damascus, including the rebel stronghold of Douma.

State media meanwhile reported that rebels had fired four shells that landed near the Russian Embassy in Damascus, without providing a casualty toll.