A U.S. court has issued a warrant for the seizure of an Iranian tanker that British Royal Marines had seized last month in Gibraltar, a court document showed on Friday.

Gibraltar's Supreme Court on Thursday ruled in favour of releasing an Iranian supertanker seized on suspicion of shipping oil to war-torn Syria in breach of international sanctions, in a blow to the United States which had tried to block the vessel's departure.

The British territory of Gibraltar will on Thursday release an Iranian oil tanker seized by Royal Marines in the Mediterranean in July, the Sun newspaper reported, citing sources close to Gibraltar Chief Minister Fabian Picardo.

President Hassan Rouhani said on Wednesday Iran and other Gulf states could protect the region's security and foreign forces were not needed, state TV reported, repeating a longstanding rejection of a U.S. maritime security mission in the region.

A highly placed Gibraltarian government source denied on Tuesday an Iranian news agency report which said the Iranian oil tanker Grace 1 would be leaving the British overseas territory on Tuesday.

Iran on Thursday hit out at Bahrain for hosting a "provocative" conference on Gulf maritime security and for its "anti-Iran" rhetoric accusing Tehran of attacking tankers in sensitive waters.

Reprieve called on its supporters to sign a petition raised to British Prime Minister Boris Johnson demanding him to interfere and call Bahrain to re-try the torture victim and death convict Maher Al-Khabbaz.

British Prime Minister Boris Johnson confirmed in a phone call with King Hamad bin Isa Al Khalifa UK's commitment to the Iran nuclear deal.

Britain on Monday joined the United States in a maritime security mission in the Gulf to protect merchant vessels travelling through the Strait of Hormuz after Iran seized a British-flagged vessel.

President Hassan Rouhani said on Thursday that Iran was ready for the worst in an uphill struggle to salvage its nuclear deal with world powers abandoned by the United States, but that he was sure Tehran would eventually prevail.

Bahrain hosted a conference on Gulf maritime security on Wednesday, after multiple attacks on shipping in the strategic Strait of Hormuz sent tensions soaring between Iran and the US.

Bahraini dissident Mousa Abed Ali climbed onto the Bahraini embassy rooftop in London in protest against the imminent execution of Ahmad Al-Malali and Ali Al-Arab.

Britain has started sending a warship to accompany all British-flagged vessels through the Strait of Hormuz, a change in policy announced on Thursday after the government previously said it did not have resources to do so.

British ministers signed off nearly £650m worth of arms license exports to Saudi Arabia in the six months following the brutal murder of the dissident journalist Jamal Khashoggi by regime forces, The Independent newspaper said.

The Swedish-based operator of the British-flagged tanker seized last week by Iran said on Tuesday it was still awaiting permission to visit the ship's 23 crew members.

Gibraltar was granted the power on Friday to detain Iran's Grace 1 oil tanker for another month, keeping the vessel at the center of a big-power quarrel between Iran and the United States and its allies.

Britain is sending its HMS Kent warship to the Gulf to protect its interests and ensure freedom of navigation after tensions with Iran, the Ministry of Defence (MoD) said on Wednesday, after earlier saying that the mission was routine.

Britain will send a third warship to the Persian Gulf, though the move is not related to the current Iran crisis, the Ministry of Defence (MoD) said on Tuesday.

Gibraltar police said on Friday that all four crew members of the Iranian Grace 1 tanker have been released on bail without charge after it was detained last week on suspicion of breaking European sanctions by taking oil to Syria.

Britain said on Friday it would deploy the destroyer HMS Duncan warship to the Gulf to replace HMS Montrose, maintaining a continuous presence there during a time of heightened tension in the region.