The U.K. government's emergency security committee has "reaffirmed" a "desire to de-escalate" but insisted Iran's military acted illegally when it seized a U.K.-flagged tanker in the Strait of Hormuz a day earlier, according to British Foreign Minister Jeremy Hunt.
"This is totally and utterly unacceptable. It raises very serious questions about the security of British shipping, and indeed international shipping, in the Strait of Hormuz," Hunt said after the July 20 meeting of the government's so-called COBR security officials.
He said Parliament would be "updated" on the situation on July 22.
The seizure of the Stena Impero and its 23 crew members, along with the nearly simultaneous detention and release of another U.K.-flagged ship, in the strategic shipping route between the Persian Gulf and the Gulf of Oman has exacerbated already high tensions between Tehran and the West amid accusations and counteraccusations for a recent spate of confrontations in the region.
Iran has so far ignored mounting European calls for it to release the ship and crew.
Reports suggested 18 Indian nationals, three Russians, a Latvian, and a Filipino were aboard the Stena Impero, which was shown at anchor in an Iranian video and said to be at the Iranian port of Bandar Abbas.
The ship's owner, Stena Bulk, said on its website on July 20 that its insurers had reached the local port authority and been told that "the crew members of our vessel...are in 'good health.'"
The Iranian official instructed them to make "a formal request...for a visit to be arranged to the crew members and vessel" and that such a request was being prepared "forthwith."
Iran's Islamic Revolutionary Guards Corps (IRGC) announced the seizure of the Stena Impero on July 19, saying the vessel had "failed to respect international maritime rules."
Reports since then have quoted Iranian authorities first suggesting the tanker's tracker had been turned off and warnings ignored, and then that the vessel had collided with an Iranian fishing boat and then ignored distress calls from the smaller ship's crew.
On July 20, Iranian Foreign Minister Mohammad Javad Zarif told Hunt by telephone that the Swedish-owned Stena Impero's detention meant it must go through a legal process before its fate is determined, according to Iranian ISNA news agency.
"Reaffirmed UK desire to de-escalate but confirmed Stena Impero was seized in OMANI waters in clear contravention of international law & discussed how 2 secure safety of UK/int shipping in Straits of Hormuz," Hunt tweeted after the COBR convened.
Earlier in the day, the European Union accused Tehran of risking "further escalation" and inhibiting efforts to defuse dangerous tensions in the strait, which is used to transit most of the Middle East's oil, as the United Kingdom and its allies sought a solution to the tanker's capture.
Another U.K.-flagged ship was reportedly detained, then released by Iranian forces on July 19.
British Defense Secretary Penny Mordaunt described the confiscation of the tanker as a "hostile act" and Iran's charge d'affaires was summoned on July 20 to the Foreign Office.
Hunt said after a phone call with Zarif on July 20 that he "expressed extreme disappointment [to Zarif] that having assured me last [Saturday] Iran wanted 2 deescalate [the] situation they have behaved in the opposite way." He vowed that "British shipping must & will be protected."
Earlier, the EU's foreign affairs office issued a statement expressing the bloc's "deep concern" at the July 19 seizures by Iran. "In an already tense situation, this development brings risks of further escalation and undermines ongoing work to find a way to resolve current tensions," it said.
"We urge the immediate release of the remaining ship and its crew and call for restraint to avoid further tensions," the 28-member EU said, adding that "freedom of navigation must be respected at all times."
Hunt has alleged that the detention of the Stena Impero is Iran's response to the detention by British forces of Iran's Grace 1 supertanker in waters off Gibraltar on July 4.
Former IRGC commander and Iranian politician Mohsen Rezai wrote on July 20 that while Tehran did not seek conflict "we are not going to come up short in reciprocating."
Iranian Foreign Minister Zarif accused the United Kingdom in a tweet of being "an accessory to #EconomicTerrorism of the US."
"Unlike the piracy in the Strait of Gibraltar, our action in the Persian Gulf is to uphold int'l maritime rules," he said. "As I said in NY, it is IRAN that guarantees the security of the Persian Gulf & the Strait of Hormuz."
The British government has not responded to a claim by the IRGC that it seized the Stena Impero despite "resistance and interference" by a British warship that it said was escorting the tanker.
The latest shipping incidents follow a month of naval brinksmanship, seizures, and reported shoot-downs of drones involving Iranian and Western forces seemingly increasingly at risk of conflict.
U.S. President Donald Trump reportedly called off a retaliatory air strike against Iran at the last minute last month after Tehran said it had downed an unmanned U.S. drone.
On July 18, Trump announced that a U.S. warship in the Strait of Hormuz had shot down an Iranian drone that defied orders to "stand down" as it approached the USS Boxer, but Tehran has insisted that it didn't lose any aircraft.
For weeks, Trump has urged other countries to condemn what he called Iranian attempts to disrupt free navigation and global commerce in the Persian Gulf region.
British, French, and German officials all decried the latest Iranian confiscations and were reportedly discussing among themselves and with U.S. officials possible responses to this weekend's incidents.
Hunt said on July 19 that while it was pursuing the return of any seized ships London had chosen the path of diplomacy and was "not looking at military options."
Iran's Press TV quoted the head of ports and maritime operations in Hormozgan Province as saying on July 20, "The investigation into the cause of the accident has been started today." He added, “All its 23 crew members will remain on the ship until the probe is over."
The U.K. has advised its shipping operators to stay out of Hormuz as the standoff continues.
Iran's economy has been hobbled by the U.S. reimposition last year of sanctions after Washington withdrew from a nuclear deal with Iran and world powers to trade international sanctions relief for curbs on Iran's disputed nuclear program.
European signatories to the 2015 agreement have vowed to try to stick with it despite the difficulties posed by tough penalties for disobeying the U.S. sanctions.
Even as Iran's IRGC was seizing the U.K.-flagged ships on July 19, Iranian and U.S. officials were publicly disputing the circumstances around a drone incident the previous day in the Strait of Hormuz, in which Trump and other U.S. officials said the U.S. military shot down an unmanned Iranian aircraft.