one of the vessels.

The US also released footage which it claimed showed boats belonging to the Islamic Revolutionary Guard Corps returning to one of the ships after the blast to remove and unexploded mine.

The attacks led to spiralling tensions around the Gulf which saw Tehran shoot down an American Navy drone, which in turn almost led to the US bombing Iran.

President Trump ordered strikes against several IRGC bases, but called them off at the final moment.

Tensions rose further last month when a Saudi refinery - the world's largest - and oil field were hit by drones and missiles, which the kingdom said were fired by Iran

The explosions shut down 5.7 million barrels per day (bpd) of production - more than 5 per cent of global oil supply.

In Mayanother four vessels were hit by explosions in the Gulf of Oman, in an attack that was also blamed on Iran. Pictured is the Norwegian Andrea Victory with a hole in its stern

Yemen's Houthi group claimed responsibility for the attacks, but a U.S. official said they originated from southwestern Iran. Riyadh blamed Tehran.

Iran, which supports the Houthis in Yemen's war, has denied any involvement.

Instability in the region was sparked when Donald Trump withdrew the US from the Iran nuclear deal, signed under Barack Obama.

The deal - which was also backed by European powers including Russia -had promised the regime economic benefits in return for curtailing its nuclear programme in a way that would stop it developing weapons.

Trump tore up the deal last year by reimposing crippling sanctions on