Yemen’s Houthi rebels have claimed they shot down another American-made MQ-9 Reaper drone, with video circulating online showing what appears to be a surface-to-air missile strike and flaming wreckage strewn across the ground.

The delicate rescue mission aimed to head off a major environmental disaster after the oil tanker was attacked by Houthi rebels off the coast of Yemen last month.

An abandoned tanker carrying more than one million barrels of crude oil could contaminate vast areas of the Red Sea in a severe, long-term environmental disaster if it breaks up or explodes, experts warn.