Masked men in black military uniform boarded a boat in coastal waters near Iran.

The ship was identified as a Marshall Islands-flagged crude oil tanker headed in the direction of Bandar-e-Jask in Iran.

The incident was flagged in an alert to the shipping industry by the United Kingdom Maritime Trade Operations (UKMTO) authority, run by the Royal Navy.

It comes amid heightened tensions in the Red Sea, as UK and US naval forces shot down missiles and drones in the Red Sea on Tuesday night, believed to be fired by the Houthis in support of Hamas.

Britain said it was considering retaliatory strikes on land targets in Yemen.

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