BEIRUT — The top UN official in Syria on Monday demanded immediate and unconditional humanitarian access to tens of thousands of people trapped in four towns, warning of starvation.

The International Committee of the Red Cross, meanwhile, released drone footage showing extensive damage to Ramadi, which was taken back from the Islamic State in December after heavy fighting that devastated much of the Iraqi city.

Aid must be allowed to reach Madaya, Zabadani, Foua, and Kafraya, the UN’s resident coordinator, Yacoub El Hillo, said in Damascus. Madaya and Zabadani, just outside the capital, are encircled by progovernment forces, while rebels are blockading Foua and Kafraya, in the country’s northwest.

The towns have been besieged since last year, with aid convoys allowed only sporadically to replenish food and medical stocks. The last delivery was made in April.

Aid group Doctors Without Borders says 16 people died in Madaya from siege conditions in January, even after aid was allowed in. El Hillo said the UN is ‘‘calling on all parties involved to ensure this doesn’t happen again.’’

Associated Press