The warplanes were also preventing any humanitarian aid reaching the buses, which included both fighters and family members including old people, injured people and pregnant women, the statement said.

Six of the buses in the IS convoy had remained in Syrian government areas, said Hezbollah, which along with the Syrian army has given the convoy safe passage as part of a ceasefire deal.

Lebanon's Hezbollah group said in a statement on Saturday that US warplanes were stopping buses in an Islamic State evacuation convoy that had left Syrian government territory from advancing further into IS areas.