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, tracking data showed on Monday.

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 showed.

The vessels’ Saudi-based operator Bahri and other Saudi officials did not immediately respond to requests ​for comment.

The tankers, each of which can carry a maximum ​of two million barrels of crude oil, had opted to re-route via ‌the Cape, taking into account the security situation, two trade sources said, based on their assessments.

Their journeys will add at least 25 additional days of sailing time if they opt ​to cross Suez ​back to ⁠Saudi ports in the Red Sea, according to Reuters calculations.

The Iran-aligned Houthis on July 20 declared ​a maritime embargo against Saudi Arabia, opening a ​new front against the US and its allies in the Iran war.

Houthi attacks in recent days on Saudi-linked ships prompted London’s marine ⁠insurance ​market last week to widen its “high ​risk” zone in the Red Sea, adding waters close to more Saudi Arabian ​ports.