The United Kingdom Maritime Trade Operations (UKMTO) agency said on Tuesday that it received a report of uncrewed aerial system activity in the vicinity of 46 nautical miles south of Yemen’s Mokha.

Authorities are investigating, UKMTO added.

Yemen’s Iranian-backed Houthi militants, who control much of Yemen, have launched wave after wave of exploding drones and missiles at commercial vessels since November 19, in what they say is a protest against Israel’s military operations in Gaza.

The Houthi campaign has been extraordinarily disruptive to international shipping, causing some companies to suspend transits through the Red Sea and instead take the much longer, costlier journey around Africa.