All hospitals in Syria's besieged rebel-held eastern Aleppo are out of service after days of heavy air strikes, its health directorate and the World Health Organisation say, though a war monitor said some were still functioning.
White House national security adviser Susan Rice said the United States condemned "in the strongest terms" the latest air strikes against hospitals and urged Russia, an ally of Syrian President Bashar al-Assad, to take steps to halt the violence.
Intense air strikes have battered the eastern part of the city since Tuesday, when the Syrian army and its allies resumed operations after a pause lasting weeks. They launched ground attacks against insurgent positions on Friday.
The war monitor, the Britain-based Syrian Observatory for Human Rights, said at least 27 people, including children, had been killed in eastern Aleppo on Saturday by dozens of air strikes and barrel bombs and dozens of artillery rounds.
Warplanes, artillery and helicopters continued bombarding eastern Aleppo on Saturday, hitting many of its densely populated residential districts, the Observatory said.
"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.
Elizabeth Hoff, the WHO representative in Syria, said on Saturday that a UN-led group of aid agencies based over the border in Turkey "confirmed today that all hospitals in eastern Aleppo are out of service".
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 de-escalate violence and facilitate humanitarian aid and access for the Syrian people," Rice said in a statement.
British Foreign Secretary Boris Johnson tweeted that reports of air strikes hitting civilians and hospitals in east Aleppo were "sickening" and called for a return to diplomacy.
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.
Health and rescue workers have previously been able to bring damaged hospitals back into operation but a lack of supplies is making that harder.