The British tanker reportedly caused damage to the fishing boat, then didn't respond to calls from the smaller craft. The fishing boat informed Iran's Ports and Maritime Organisation, which notified the Revolutionary Guard. IRNA reported that the Revolutionary Guard vessels directed the Stena Impero to an Iranian port for an investigation Friday.

Iran's attempt to offer a "technical" explanation for seizing the tanker could signal a possible de-escalation of tensions in the strategic Strait of Hormuz, which has become a flashpoint between Tehran and the West.

Another British ship was briefly detained by Iran on Friday before being allowed to go.

The seizing of the British tanker marked perhaps the most significant escalation since tensions between Iran and the West began rising in May. At that time, the US 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 manoeuvre bringing fear that any misunderstanding or misstep by either side could lead to war.

Details of what took place Friday remained sketchy after Iran reported that it had seized a British oil tanker in the Strait of Hormuz. The strait at the mouth of the Persian Gulf is a shipping channel for one-fifth of all global crude exports.

The Revolutionary Guard said Friday that the Stena Impero had been taken into port because it was not complying with "international maritime laws and regulations."

A statement from Stena Bulk, which owns the seized tanker, said it was unable to make contact with the ship after it was approached by unidentified vessels and a helicopter in international waters. A spokesman for the company's owners said the tanker was in "full compliance with all navigation and international regulations."

The company said the tanker had 23 crew members of Indian, Russian, Latvian and Filipino nationalities and there were no reports of any of them were injured.

The UK has featured prominently in the recent tensions with Iran. Britain's Royal Marines assisted in the seizure of an Iranian oil supertanker on July 4 by Gibraltar, a British overseas territory off the southern coast of Spain.

Britain said it would release the vessel if Iran could prove it was not breaching European Union sanctions on oil shipments to Syria.

Gibraltar's government said Friday that its Supreme Court had extended by 30 days the detention of the Panama-flagged Grace, which was loaded with over 2 million barrels of Iranian crude oil.

British Foreign Secretary Jeremy Hunt initially said two ships were seized Friday 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. Iran's semi-official Fars news agency tweeted that the Mesdar had left Iran's territorial waters.

Hunt called the seizures "unacceptable" and stressed the importance of freedom of navigation, as he prepared to enter an emergency government meeting Friday night.

"We're not looking at military options, we're looking at a diplomatic way to resolve the situation, but we are very clear that it must be resolved," Hunt later told Sky News, warning that if the situation is not resolved quickly "there will be serious consequences."

President Donald Trump said US officials would talk with Britain about the unfolding crisis.

"This only goes to show what I'm saying about Iran: Trouble, nothing but trouble," he said.

Central Command said the US has intensified air patrols over the Strait of Hormuz in response to the seizure.

The incident came two days after Washington claimed that a US warship downed an Iranian drone in the strait. Iran denied that it lost an aircraft in the area.

On June 20, Iran shot down an American drone in the same waterway, and Trump came close to retaliating but called off an airstrike at the last moment.

Tensions in the region have been escalating since Trump withdrew the US 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, pressuring the other partners in the nuclear deal, particularly European nations, to pressure the US to lift the crippling sanctions.

Australian Associated Press