More than 20 tankers have taken costly detours away from the Red Sea because of the threat of attacks from Iran-backed Houthi rebels amid a sharp decline in traffic through the Bab al-Mandab strait, according to ship tracking and reports.

Data analyst Kpler identified Greek, Norwegian, Chinese and Singaporean-operated crude, product and chemical tankers among those that had diverted from previously planned routes, with many travelling to Europe via the southern tip of Africa.