‘Long-planned movement’, says UK as Iran’s supreme leader vows response to Britain’s ‘piracy’ of its oil tanker.

The United Kingdom will send a third warship to the Gulf, though the move is not related to the current Iran crisis, the country’s Ministry of Defence (MoD) has said.

The move came as Iran’s supreme leader Ayatollah Khamenei upped the ante in a volatile standoff with the United States, warning Tehran would continue removing restraints on its nuclear programme and retaliate for the seizure of an Iranian oil tanker.

The UK’s MoD said on Tuesday HMS Duncan, a type 45 frigate, is transiting to the region to ensure Britain maintains a continuous maritime security presence while HMS Montrose, a type 23 frigate, undertakes planned maintenance.

Later in the year, HMS Kent, another type 23 frigate, will deploy to the region, taking over from HMS Duncan. It said that support ship RFA Wave Knight will deploy to the Gulf at the start of August.

“These long-planned movements do not reflect an escalation in the UK posture in the region and are routine,” the MoD added.

Meanwhile, Khamenei said on Tuesday Tehran would respond to Britain’s “piracy” over the seizure of the Iranian oil tanker in Gibraltar earlier this month.

“Evil Britain commits piracy and steals our ship … and gives it a legal appearance. The Islamic Republic … will not leave this wickedness unanswered and will respond to it at an appropriate time and place,” Khamenei said.

Following his remarks, a spokesman for UK’s Prime Minister Theresa May said an escalation of tensions between the Western states and Iran was in no one’s interest. “[…] we have repeatedly stressed that to the Iranians,” the spokesman said.

Iran has called on Britain to immediately release its oil tanker, which was detained by British Royal Marines on the suspicion that it was breaking European sanctions by taking oil to Tehran’s close ally Syria.

The affair has stoked tension in the Gulf, with Britain saying on July 11 that it had fended off Iranian ships that tried to block a British tanker heading through the area.

Tensions have spiked since US President Donald Trump last year abandoned a 2015 nuclear deal with Iran under which Tehran had agreed to curtail its enrichment of uranium in return for the lifting of global sanctions crippling its economy.

On Monday, European parties to the pact decided not to trigger the deal’s dispute mechanism in favour of pursuing more talks and avert any US-Iran military conflict, but took no action to shield Iran against a sanctions clampdown by Trump.

Khamenei has accused Britain, Germany and France of failing to uphold obligations under the deal to restore Iranian access to global trade, especially for Tehran’s oil exports blocked by US sanctions.