DUBAI, July 22 -- Two supertankers carrying 2.8 million barrels of Saudi crude turned north in the Red Sea on Tuesday, reversing course toward the Suez Canal rather than continuing south through the Bab al-Mandeb strait, as shipping data showed the first concrete evidence that Yemen's Houthi movement has begun enforcing the naval blockade it declared against Saudi Arabia a day earlier.

The tankers Rodos and Xin Long Yang, both loaded at Yanbu port on Saudi Arabia's Red Sea coast, had been on a standard Asia-bound heading before their AIS signals bent northward, according to vessel-tracking data reviewed by Al Jazeera. The reversal came after Houthi authorities threatened to attack any vessel transiting Bab al-Mandeb to or from Saudi port...