Britain has already sent the HMS Duncan, an air defence destroyer, to cover for frigate HMS Montrose while it undergoes maintenance in nearby Bahrain, and will also send frigate HMS Kent "later this year".

Reports said it would head to the Gulf in mid-September.

HMS Montrose last week warned off three Iranian gunboats that UK officials said were trying to "impede" the progress of a British supertanker through the Strait of Hormuz in the Gulf.

The defence ministry said the HMS Kent would be "taking over" from HMS Duncan, but added that an "occasional overlap of ships when one deployment begins and another ends... is not uncommon," suggesting that all three could be in the region at some point.

The ministry said the deployments were "long-planned" to ensure "an unbroken presence" in the crucial waterway and "do not reflect an escalation in the UK posture in the region".

Iranian officials have denied last Wednesday's incident in the Strait of Hormuz ever happened.

The British government has in any case raised the alert level for ships travelling through Iranian waters to three on a three-point scale, indicating a "critical" threat.

HMS Duncan is an air defence destroyer that carries a set of heavy Harpoon anti-ship missiles and has a company and crew in excess of 280.

Tensions have been escalating in the region for weeks, with US President Donald Trump last month calling off at the last minute an air strike on Iran over its downing of a US spy drone.

The Strait of Hormuz episode occurred a week after UK Royal Marines helped the Gibraltar authorities detain an Iranian tanker that US officials believe was trying to deliver oil to Syria in violation of separate sets of EU and US sanctions.

Iran has bristled at the arrest and issued a series of increasingly ominous warnings to both the United States and Britain about its right to take unspecified actions in reprisal.

British Foreign Secretary Jeremy Hunt sought to ease tensions on Monday by saying the tanker would be released if Tehran guaranteed it was not heading to Syria.