Spokesman of Iran's Guardian Council, Abbas Ali Kadkhodaei, was quoted in the semi-official Fars news agency saying "the rule of reciprocal action is well-known in international law" and that Iran's moves to "confront the illegitimate economic war and seizure of oil tankers is an instance of this rule and is based on international rights."
The council rarely comments on state matters, but when it does it is seen as a reflection of the supreme leader Ayatollah Ali Khamenei's views. That's because the council works closely with Khamenei, who has final say on all state matters.
The British-flagged Stena Impero with 23 crew aboard was seized by Iran late Friday. Maritime trackers show it was headed to a port in Saudi Arabia.
On July 4, Britain's Royal Marines took part in the seizure of an Iranian oil tanker carrying more than 2 million barrels of Iranian crude oil by Gibraltar, a British overseas territory off the southern coast of Spain. Officials there initially said the seizure happened on orders from the U.S.
Britain has said it would release the vessel if Iran could prove it was not breaching European Union sanctions on oil shipments to Syria. However, on Friday, a court in Gibraltar extended by 30 days the detention of the Panama-flagged Grace.
The state-run news agency IRNA had reported earlier Saturday that Iran had seized the British-flagged vessel late Friday after it rammed an Iranian fishing vessel — an explanation that portrayed the seizure as a technicality rather than a tit-for-tat move in the current tense climate.
In London, Tom Tugendhat, the chairman of Britain's House of Commons Foreign Affairs Committee, said military action to free the tanker would be "extremely unwise," especially because the vessel was apparently taken to a well-protected port.
Tensions between Iran and the West had been rising since May, when the U.S. announced it was dispatching an aircraft carrier and additional troops to the Middle East, citing unspecified threats posed by Iran.
The ongoing showdown has caused jitters around the globe, with each maneuver bringing fear that any misunderstanding or misstep by either side could lead to war.
The seizing of the tanker late Friday was seen as a significant escalation.
British Foreign Secretary Jeremy Hunt initially said two ships were seized in the Strait of Hormuz, the second sailing under a Liberian flag.
The owner of the Liberian-flagged tanker later said the ship was briefly boarded by armed guards before being allowed to go.
Stena Bulk, the owner of the seized British tanker, said the vessel had 23 crew members of Indian, Russian, Latvian and Filipino nationalities and there were no reports any of them were injured. The Indian and Philippine governments have said they're working to get Iran to release nationals from the two countries who were on board the ship.
Iranian officials say the crew is inside the tanker.
The comments by the Guardian Council reflect how prominently Britain has featured in the rising tensions with Iran.
There was a brief standoff between the British navy and the Iranian Revolutionary Guard vessels recently. The British navy said it warned three Guard vessels away after they tried to impede the passage of a commercial British tanker that the navy was escorting.
The current tensions have been escalating since President Donald Trump withdrew the U.S. last year from Iran's 2015 nuclear deal with world powers and imposed sweeping economic sanctions on Iran, including its oil exports.
The sanctions have hit the Iranian economy hard.
Iran's government has desperately tried to get out of the chokehold, urging the other partners in the nuclear deal, particularly European nations, to pressure the U.S. to lift the crippling sanctions.
Meanwhile, crude oil prices climbed following Iran's announcement about the Stena Impero as traders worried the escalating tensions could affect crude supplies.
Maritime security in the Strait of Hormuz has deteriorated in recent weeks after six attacks on oil tankers that the U.S. has blamed on Iran — an allegation the Islamic Republic denies.
The U.S. has asked Mideast allies like Saudi Arabia and the United Arab Emirates in past weeks to contribute financially and militarily to a Trump administration proposal called the Sentinel Program — a coalition of nations working with the U.S. to preserve maritime security in the Persian Gulf and keep eyes on Iran.
Late Friday, officials said the U.S. is sending several hundred troops as well as aircraft and air defense missiles to Saudi Arabia as part of its increased military presence in the region. The move has been in the works for many weeks and is not a response to Friday's seizure by Iran of a British tanker.
King Salman approved hosting U.S. armed forces in the kingdom "to increase joint cooperation in defense and regional security and stability," a statement in the state-run Saudi Press Agency said.