A damaged ambulance is pictured after an airstrike on the rebel-held town of Atareb, in the countryside west of Aleppo. Photograph:( Reuters )
All hospitals in the Syrian city of Aleppo are out of service due to the wave of air strikes in recent days, the World Health Organisation said.
Health services have been crippled in the ravaged city after forces loyal to the Syrian government and its allies resumed bombing from Tuesday after several weeks of calm.
The latest crisis has prompted the United States to condemn the attacks and urge the Syrian government and Russia to halt them.
Syrian Observatory for Human Rights, a Britain-based war monitor, said at least 27 people, including children, had been killed in eastern Aleppo -- an area that has been occupied by forces that are loyal to the US -- on Saturday.
Warplanes, artillery and helicopters continued bombarding eastern Aleppo on Saturday, hitting many of its densely populated residential districts, the Observatory said. There were intense clashes in the Bustan al-Basha district, it added.
"This destruction of infrastructure essential to life leaves the besieged, resolute people, including all children and elderly men and women, without any health facilities offering life-saving treatment ... leaving them to die," said Aleppo's health directorate in a statement sent to Reuters late on Friday by an opposition official.
The monitoring group said some hospitals were still operating in besieged parts of Aleppo but said many residents were frightened to use them because of the heavy shelling.
Medical sources, residents and rebels in eastern Aleppo say hospitals have been damaged by air strikes and helicopter barrel bombs in recent days, including direct hits on the buildings.
"The United States again joins our partners ... in demanding the immediate cessation of these bombardments and calling on Russia to immediately deescalate violence and facilitate humanitarian aid and access for the Syrian people," Rice said in a statement.
Both Russia and Assad's government have denied deliberately targeting hospitals and other civilian infrastructure during the war, which began in 2011 and was joined by Russia's air force in September 2015.
The charity Doctors Without Borders said in a message there had been more than 30 hits on hospitals in eastern Aleppo since early July. "Doctors are few and medical supplies are depleted, with no possibility of sending more supplies in," it said.
Health and rescue workers have previously been able to bring damaged hospitals back into operation but a lack of supplies is making that harder.
The Syrian war pits Assad and his allies Russia, Iran and Shi'ite militias against Sunni rebels including groups supported by the United States, Turkey and the Gulf monarchies and also jihadist groups.
Aleppo, for years split between a rebel-held east and government-held western sector, has become the fiercest front. During the summer, pro-government forces managed to besiege the districts held by insurgents which are home to about 270,000 people, according to the United Nations.
Syrian state television said on Tuesday the air force had targeted "terrorist strongholds and supply depots" in Aleppo. Russia has said its air force is only conducting air strikes in other parts of Syria. The Damascus government describes all the rebels fighting it as terrorists.
An army offensive backed by a major aerial bombardment from late September to late October killed hundreds, according to the United Nations, and tightened the siege, leaving eastern Aleppo with little food, medicine or fuel.
A rebel counter-attack early this month involved shelling that killed dozens of civilians, the U.N. said, but it quickly petered out and the army and its allies, including Hezbollah and Iraqi militias, reversed all insurgent gains in about two weeks.