DUBAI (REUTERS) - Iran on Sunday (July 21) urged Britain to contain "domestic political forces" intent on escalating tensions between the two countries following Iran's seizure of a British-flagged oil tanker.

Britain has called Iran's capture of the Stena Impero in the Gulf on Friday a "hostile act" and rejected Teheran's explanation that it seized the vessel because it had been involved in an accident.

Iran's top diplomat said on Sunday that only "prudence and foresight" could alleviate tensions between his country and Britain.

"Having failed to lure @realDonaldTrump into War of the Century, and fearing collapse of his #B-Team, #AmbJohnBolton is turning his venom against the UK in hopes of dragging it into a quagmire," Mr Mohammad Javad Zarif said on Twitter.

"Only prudence and foresight can thwart such ploys."

The "UK government should contain those domestic political forces who want to escalate existing tension between Iran and the UK well beyond the issue of ships. This is quite dangerous and unwise at a sensitive time in the region", Iran's envoy to Britain Hamid Baeidinejad said on Twitter.

"Iran however is firm and ready for different scenarios," he said.

A day earlier, British Foreign Minister Jeremy Hunt said Teheran's actions showed "worrying signs Iran may be choosing a dangerous path of illegal and destabilising behaviour after Gibraltar's legal detention of oil bound for Syria".

The crew of the tanker seized by Iran's Revolutionary Guards are all safe, the head of the Ports and Maritime Organisation in Hormozgan Province told state TV on Sunday.

"All 23 crew members aboard the ship are safe and in good health in Bandar Abbas port," Mr Allahmorad Afifipour said.

SANCTIONS

Mr Afifipour said the seized tanker "risked maritime safety" in the Strait of Hormuz, through which almost a fifth of the world's annual oil consumption passes.

"We are required by regulations to investigate the issue... the duration of the investigation depends on the level of cooperation by the involved parties," said Mr Afifipour.

The seizure has heightened tension between Iran and Britain, which is a party to Iran's 2015 multinational nuclear deal.

The Daily Telegraph newspaper reported on Saturday that London was planning to target Iran with sanctions in the aftermath of the tanker seizure.

In a letter to the UN Security Council, Britain said the tanker was approached by Iranian forces in Omani territorial waters where it was exercising its lawful right of passage, and that the action "constitutes illegal interference".

Stena Bulk, the vessel's Sweden-based owners, said it is preparing a formal request to visit the crew, who are from India, Latvia, the Philippines and Russia.

India has called on Iran to release the 18 Indian crew members.

Teheran for weeks has vowed to retaliate for the seizure by Royal Marines of the tanker Grace 1 carrying Iranian oil near Gibraltar on July 4 over suspicion of violating sanctions on Syria.

"The Revolutionary Guards responded to Britain's hijacking of the Iranian tanker," Parliament Speaker Ali Larijani told a Parliament session aired live on state radio.

US President Donald Trump pulled the United States out of the nuclear agreement with Iran last year and reimposed and tightened sanctions on Iran's oil and banking sectors.

WAIVERS

Waivers allowing eight countries to keep buying Iranian oil - China, Greece, India, Italy, Japan, South Korea, Taiwan and Turkey - expired on May 2.

Iran has repeatedly threatened to close the Strait of Hormuz if it cannot export its oil because of the sanctions, but cannot legally do so as part of the waterway is in Oman's territorial waters.

Oman has urged Iran to release the Stena Impero, calling on all parties to exercise restraint and resolve differences diplomatically, state broadcaster Oman TV News reported on Sunday.

Ships using the Strait also pass through Iranian waters, which are under the responsibility of Iran's Revolutionary Guards Navy.

"Iran is displaying its power without entering a military confrontation. This is the result of America's mounting pressure on Iran," said an Iranian official, who asked not to be identified.

Junior defence minister Tobias Ellwood said on Sunday Britain was looking into a series of options to respond to Iran's seizure of the British-flagged tanker. "We will be speaking with our colleagues, our international allies, to see what can actually be done," he told Sky News.

"Our first and most important responsibility is to make sure that we get a solution to the issue to do with the current ship, make sure other British-flagged ships are safe to operate in these waters and then look at the wider picture," he sais.

Britain also summoned the Iranian charge d'affaires in London.

Iran's Fars news agency said the Guards had taken control of the Stena Impero on Friday after it collided with an Iranian fishing boat whose distress call it ignored.

Mr Zarif told Britain's Hunt that the ship must go through a legal process before it could be released, Iran's ISNA news agency reported.

The United States, which tightened sanctions against Iran in May with the aim of halting its oil exports altogether, has been warning for months of an Iranian threat to shipping in the strait.

Another oil tanker, the Mesdar, was also boarded by Iranian personnel on Friday and temporarily forced to divert towards Iran, but later was allowed to continue on its route through the strait. On Saturday Algeria's APS news agency said the Mesdar was owned by Algeria's state oil company Sonatrach.

France, Germany and the European Union have joined Britain in condemning the seizure.