Tensions between the UK and Iran escalated in the Persian Gulf on Wednesday when five Iranian ships apparently attempted to seize a British oil tanker.

The UK-flagged tanker British Heritage was crossing into the Strait of Hormuz when it was approached by the fleet of Iranian Islamic Revolutionary Guard Corps boats, which radioed in and asked it to change course and move into Iranian waters, US officials told CNN.

A British frigate, HMS Montrose, was five miles away and monitoring the tanker’s route.

It sped toward the tanker and got between it and the five Iranian boats, US officials told ABC News.

The warship’s crew radioed the Iranians and warned them to back off, which they did.

The incident comes after Iranian President Hassan Rouhani on Wednesday warned Britain would face “consequences” over the seizure of an Iranian tanker.

The ship, seized last week off the coast of Gibraltar, apparently was carrying oil to Syria in violation of international sanctions.

The US has accused Iran of attacking several oil tankers in the region in May and June.