GENEVA (Reuters) - Unverified reports say 15 to 20 people died of starvation in the Syrian city of Deir al-Zor last year, the United Nations said on Saturday, warning that 200,000 residents there face a severe food shortage and sharply deteriorating conditions.

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Western parts of the city have been under siege by Islamic State militants since last March, leaving inhabitants with no electricity for more than 10 months and a water supply for only three hours a week, the U.N. said in a report.

Deir al-Zor is the most populous of about 15 besieged areas in Syria, where about 450,000 people are trapped and cut off from aid by the government, Islamic State and other insurgent groups involved in the country’s civil war.

Another besieged population, 42,000 people trapped in the town of Madaya, has received two convoys of aid supplies this month, but local aid workers have reported 32 deaths from starvation.

There have been no flights into the Deir Al-Zor airport except by helicopter since September and malnutrition is widespread, according to the United Nations.

“Severe cases of malnutrition are reported by health personnel particularly amongst children with unverified reports of 15 – 20 people dying from starvation in 2015 (of whom four were children),” it said.

“All schools are functioning in the city however absenteeism amongst children is common as children suffer from frequent fainting due to malnutrition,” it added.

Islamic State militants “interrogate and harass people leaving the city and confiscate their documents”, while the Syrian government “requires those wishing to leave by land or air to obtain authorisation”, the report said.

A government grain reserve and a very small patch of government-controlled land can continue to provide grain for two main functioning bakeries for “many months”, but a lack of fuel and yeast has boosted black market bread prices to eight times the price in the capital, Damascus.

“Families have to queue for hours to get their share of bread with the majority of inhabitants surviving on bread and water,” said the report from the U.N. Office for the Coordination of Humanitarian Affairs (OCHA).

The Syrian government airlifted “a limited amount of basic commodities” last Monday, including food to be sold at Damascus prices, the U.N. said. Russia said on Friday it had dropped 22 tonnes of aid to the besieged part of the city.

Of those under siege in the city, 70 percent are women and children, and many have been displaced from their homes elsewhere and are living in temporary shelters. None of the health centres are functioning and there have been reports of cases of Leishmaniasis and Typhoid, the report said.