A convoy of Islamic State fighters began a new attempt to reach territory held by the militant group in eastern Syria on Thursday after being blocked by U.S.-led airstrikes, despite warnings of more military action.

More than 300 lightly armed IS fighters and about 300 family members are being evacuated from Syria's western border with Lebanon under a cease-fire agreement involving the ultra-hardline group, the Syrian army and the Lebanese Shiite group Hezbollah.

But the U.S.-led coalition fighting IS in Syria opposes experienced combatants being transferred to a battle zone in which it is active, and used warplanes on Wednesday to halt the convoy by damaging the road ahead. Coalition jets also struck fighters on their way to meet the convoy.