Health facilities have repeatedly been targeted during the country's brutal civil war, a pattern that has continued in a ferocious government assault launched last Tuesday to recapture eastern Aleppo.
"There are currently no hospitals functioning in the besieged area of the city," the World Health Organization (WHO) said in a statement on Sunday, citing reports from its partners in the area.
"More than 250,000 men, women and children living in eastern Aleppo are now without access to hospital care," the United Nations agency added.
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WHO noted that some health services in the devastated area "are still available through small clinics", but that trauma care, major surgeries and other responses to serious conditions have stopped.
UN agencies, including WHO, have been barred from entering eastern Aleppo since July when regime troops seized the last access route, leaving the area cut off from food and medical aid for more than four months.
UN Syria envoy Staffan de Mistura, whose efforts to negotiate aid access to eastern Aleppo have repeatedly fallen flat, warned Sunday that time was running out to avoid a humanitarian catastrophe.
Civilians in the city's government-controlled west have also been hit in deadly rebel attacks, but the area has continued to receive humanitarian supplies.