Six Saudi-flagged supertankers have changed course in the Gulf of Aden in recent days and are heading to southern Africa, following threats by Yemen’s Houthi movement to target Saudi shipping, Reuters reports, citing tracking data.

The tankers, which were empty of cargo after returning from destinations in Asia, were sailing in formation towards southern Africa, rather than opting to transit the southern Red Sea via the Bab el-Mandeb chokepoint, according to AIS ship-tracking on LSEG and MarineTraffic.

One of the tankers, Dilam, had Gibraltar as its destination, ship tracking shows.

The vessel’s Saudi-based operator, Bahri, and other Saudi officials have not immediately responded to requests for comment.