Iran Guards seize British-flagged tanker in Strait of Hormuz
Britain however said Iran had seized two ships in the Gulf, with Foreign Secretary Jeremy Hunt warning of "serious consequences" if the issue was not resolved quickly.
The British owner of one of the tankers, the Liberian-flagged Mesdar, said the ship had been temporarily boarded by armed personnel, but was now free to leave.
The latest incident came as President Donald Trump insisted Friday that the US military had downed an Iranian drone that was threatening an American naval vessel in the Strait of Hormuz, despite denials from Tehran.
The Stena Impero tanker "was confiscated... for failing to respect international maritime rules," the Guards official website Sepahnews said.
The tanker "was led to the shore and handed over to the organisation to go through the legal procedure and required investigations," it said.
Tanker tracking service Marine Traffic showed that the Swedish-owned Stena Impero last signalled its location near the Island of Larak in the highly sensitive waterway at 9:00 PM local time (1630 GMT).
The ship was transiting the Strait of Hormuz and in "international waters" when it was "attacked by unidentified small crafts and a helicopter," the owner said.
"We are presently unable to contact the vessel which is now tracking as heading north towards Iran," a statement said.
Hunt said he was "extremely concerned" by the seizure of two vessels in the Strait -- through which nearly a third of the world s oil is transported.
"We are absolutely clear that if this situation is not resolved quickly there will be serious consequences," he told Sky News ahead of an emergency ministerial COBRA meeting.
Britain confirmed that one of the boats seized was British-registered.
Norbulk Shipping, the owner of the other vessel said it was now free to continue its voyage with all crew "safe and well".
The company said the Mesdar was boarded by armed personnel at around 1630 GMT, but they had left by 2000 GMT.
Iran's Fars News Agency reported that senior military officials rejected reports that the Liberian-flagged tanker has been seized, stressing that the Stena Impero was the only foreign ship under Iranian custody.
The incident came hours after Gibraltar s Supreme Court said it would extend by 30 days the detention of an Iranian tanker seized two weeks ago on allegations that it was heading to Syria in violation of sanctions.
Tensions in the Gulf have soared in recent weeks, with Trump calling off air strikes against Iran at the last minute in June after Tehran downed an American drone, and blaming Iran for a series of tanker attacks -- charges the Islamic Republic denies.
Hours before the latest incident, Iran and the US were caught in a new war of words.
Trump on Friday reiterated a claim that Washington brought down an Iranian drone that was threatening an American vessel, the USS Boxer in the Strait of Hormuz.
Iran categorically denied the allegation and deputy foreign minister Abbas Araghchi tweeted that American forces may have shot down a US drone by mistake.
Trump's National Security Advisor John Bolton said there was "no question that this was an Iranian drone".
The Revolutionary Guards released a video Friday which they said belies the US claims.
The seven-minute-long footage, apparently shot from high altitude, shows a convoy of ships which the Guards said they were tracking as they passed through the Strait of Hormuz.
The vessels in the footage could not be immediately identified, although one looks similar to the USS Boxer.
Earlier a US official said Washington has "very clear evidence" that it downed the drone but gave no further details.
"If you fly too close to our ships, you re going to get shot down," the official said.
As tensions soar, Tehran's arch rival Saudi Arabia announced Friday that it would once again host US troops on its soil to boost regional security, its defence ministry said.
The latest escalation comes more than a year after Washington unliterally withdrew from the 2015 Iran nuclear agreement and began ratcheting up sanctions against Tehran.
On Friday Trump spoke with French leader Emmanuel Macron, the White House said, with the leaders discussing "ongoing efforts to ensure Iran does not obtain a nuclear weapon."
Earlier this month, Iran purposely overshot the deal's caps on uranium enrichment, aiming to pressure the remaining parties to make good on their promises to help prop up its economy.
Iran has repeatedly threatened to close the Strait of Hormuz if it is attacked.