A third round of aid was delivered to besieged Syrian towns on Monday, although armed groups postponed one humanitarian team's access saying they needed more time to make security arrangements, the United Nations said in a joint statement.

The UN, the International Committee of the Red Cross (ICRC) and the Syrian Arab Red Crescent (SARC) made deliveries to the towns of Zabadani and Madaya, which are near the Lebanese border and surrounded by government forces, and to Foua and Kafraya in Idlib province, which are surrounded by rebel groups.

Aid to the towns, where people are reported to have died of starvation, was granted earlier this month as part of a deal following long negotiations between warring sides and humanitarian agencies.

UN, ICRC and SARC teams on Monday delivered fuel to Madaya, Foua and Kafraya, and delivered food and medical supplies to Zabadani.

But a joint team which wanted to assess the situation in Foua and Kafraya was not able to enter these villages on Monday.

"The joint team had to postpone the mission to Foua and Kafraya upon receipt of reports from armed groups that more time was needed to finalize security arrangements in areas under their control," the joint statement said, adding that they will continue efforts to reach the town.