People carry posters during a sit-in calling for the lifting of the siege off Madaya, in front of the International Committee of the Red Cross in Beirut, Lebanon January 8, 2016.

Humanitarian groups could begin delivering much-needed aid in three besieged Syrian towns as early as Sunday, spokesmen said on Friday.

The International Committee of the Red Cross (ICRC) and U.N. World Food Programme (WFP) said they were preparing convoys packed with food and medical supplies for suffering populations in the towns of Madaya, al-Foua and Kefraya.

As Syria reels from civil war, a six-month-long blockade of Madaya by the Syrian army and its Lebanese ally, Hezbollah, has trapped about 40,000 residents now enduring a harsh winter.

Further north, the villages of al-Foua and Kefraya, in the Idlib governorate, are home to some 20,000 residents under siege by armed opposition groups.

Twenty-three people have died of starvation in Madaya since Dec. 1 at health centers supported by Medecins Sans Frontieres (MSF), the global medical aid group said.

Aid deliveries could start on Sunday or Monday as documentation is being prepared, said Pawel Krzysiek, a spokesman for the ICRC in Syria, speaking from Damascus.

The trips could be dangerous as the convoys cross battle lines, he said.

“Basically we’ll be crossing from the territory controlled by one side to the territory controlled by another,” Krzysiek said. “As you can imagine it is always a very, very sensitive operation.”

The first U.N. convoy could set off as early as Sunday, said WFP spokeswoman Abeer Etefa.

Urgently needed supplies include medicine and baby formula because mothers of infants are not lactating due of hunger, said Krzysiek.

The WFP will distribute such staples as rice, vegetable oil, flour, sugar, salt and canned food.

Blockades have been a common feature of the nearly five-year-old civil war that has killed an estimated 250,000 people, with government forces besieging rebel-held areas and rebel groups blockading loyalist areas.

Siege warfare has been used in Syria “in a ruthlessly coordinated and planned manner” with the aim of “forcing a population, collectively, to surrender or suffer starvation,” a U.N. commission of inquiry has said.

A U.N. Security Council resolution adopted on Dec. 18 setting out a road map for peace talks called on the parties to allow aid agencies unhindered access throughout Syria, particularly in besieged and hard-to-reach areas.

A newly formed opposition council set up to oversee negotiations has said aid must be delivered before talks that are planned for Jan. 25.

This will be the second humanitarian convoy reaching the three towns. The first took place in October.

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