The Grace One supertanker, carrying 2.1 million barrels of oil, was intercepted by British Royal Marines and Gibraltar's police as it transited through waters claimed by Gibraltar, which is located on Spain's southern tip.

In a statement, Picardo's government said the meeting took place on Wednesday and to discuss the continued detention of the Grace One tanker "and to seek to de-escalate all aspects of the issues arising".

"constructive and positive" meeting with Iranian officials in London aimed at defusing tensions around an oil tanker carrying Iranian oil being held in the British territory's waters.

US officials believed the tanker was destined for Syria to deliver oil, in violation of separate sets of EU and US sanctions.

Iran has reacted with fury at what it termed "piracy" and warned it would not let the interception go unanswered.

Last week, a British warship in the Gulf warned off armed Iranian boats that tried to stop a UK supertanker. London has since announced the deployment of two more warships to the Gulf region for the coming months.

Increased concern in the Gulf

British Foreign Secretary Jeremy Hunt last weekend said he held talks with his Iranian counterpart Mohammad Javad Zarif about the Grace One that he also termed "constructive". He tweeted that he promised he would "facilitate" the release of the tanker "if we received guarantees that it would not be going to Syria".

An order by Gibraltar's supreme court authorising the detention of the Grace One tanker lapses after Friday, though it can be renewed for up to three months.

Iran on Thursday announced it had seized a foreign tanker in international waters in the Strait of Hormuz at the entrance to the Gulf, claiming it was involved in "fuel smuggling". Video it released showed the vessel to be the MT Riah, a Panama-flagged ship whose ownership has not been established.

The US military, which maintains a naval base in

the Gulf and regularly patrols the area, said it will work "aggressively" with allies to ensure safe civilian shipping in the region.

Bahrain said Thursday it will host a conference on "maritime and air navigation security" and "find ways to deter the Iranian threat and ensure freedom of navigation in this strategic region", the Gulf kingdom's BNA state news agency said.

The Strait of Hormuz is the conduit for nearly a third of the world's crude oil.

Bahrain, which hosts the US Fifth Fleet, said it would co-host the conference with the US and Poland. It did not specify a date for the meeting.