Iran’s supreme leader Ayatollah Ali Khamenei has accused Britain of “theft” and “piracy” over the seizure of an Iranian oil tanker off the coast of Gibraltar, saying Iran would “not leave such evil deeds unanswered.”

The comments came during a televised address, as concerns grew about a UAE-based Gulf oil tanker, the MT Riah, which went missing in the Strait of Hormuz on Saturday.

A US defence official said on Tuesday the US “has suspicions” the tanker has been seized by Iran, saying it disappeared near Qeshm, an island with an Iranian Revolutionary Guard base.

Tensions between Iran and the UK have escalated since the Iranian Grace 1 oil tanker was seized by British Royal Marines earlier this month off the coast of Gibraltar.

The supertanker, which was carrying 2.1m barrels of light crude oil, was detained on suspicion of violating EU sanctions by transporting the oil to Syria.