A U.S. warship on Thursday destroyed an Iranian drone in the Strait of Hormuz after it threatened the ship, U.S. President Donald Trump said. The encounter marked a new escalation of tensions between the countries less than one month after Iran downed an American drone and Trump came close to retaliating with a military strike.

In remarks at the White House, Trump blamed Iran for a "provocative and hostile" action and said the U.S. responded in self-defence.

He said the navy's USS Boxer, an amphibious assault ship, took defensive action after the Iranian aircraft closed to within 1,000 yards of the ship and ignored multiple calls to stand down.

"The United States reserves the right to defend our personnel, facilities and interests and calls upon all nations to condemn Iran's attempts to disrupt freedom of navigation and global commerce," Trump said.

The Pentagon said the encounter happened at 10 a.m. local time Thursday in international waters while the Boxer was heading to the Persian Gulf.

"A fixed-wing unmanned aerial system [UAS] approached Boxer and closed within a threatening range," chief Pentagon spokesman Jonathan Hoffman said in a written statement. "The ship took defensive action against the UAS to ensure the safety of the ship and its crew."

Iranian Foreign Minister Mohammad Javad Zarif said Iran has no information about losing a drone.

Foreign tanker seized

Earlier on Thursday Iran said its Revolutionary Guard seized a foreign oil tanker and its crew of 12 for smuggling fuel out of the country, and hours later released video showing the vessel to be a United Arab Emirates-based ship that had vanished in Iranian waters over the weekend.

The announcement solved one mystery — the fate of the missing ship — but raised a host of other questions and heightened worries about the free flow of traffic in the Strait of Hormuz, one of the world's most critical petroleum shipping routes. One-fifth of global crude exports passes through the strait.

The incident happened with tensions running high between Iran and the United States over Trump's decision to pull the U.S. out of the Iran nuclear deal.

This undated photo provided by Iranian state television's English-language service, Press TV, shows the Panamanian-flagged oil tanker MT Riah surrounded by Iranian Revolutionary Guard vessels. Iran said its Revolutionary Guard seized a foreign oil tanker and its crew of 12 for smuggling fuel out of the country. (Press TV via The Associated Press)

Iranian state television did not at first identify the seized vessel but said it was intercepted on Sunday and was involved in smuggling some one million litres of Iranian fuel. Iran did not identify the nationalities of the crew.

Crude prices, which had been falling since last week, ticked higher almost immediately after the announcement.

Iran said the tanker was seized south of its Larak Island in the Strait of Hormuz. Neighbouring Qeshm Island has a Revolutionary Guard base.

Hours after the initial report, Iranian TV released footage of the ship surrounded by Guard vessels and showed the registration number painted on its bridge, matching that of the U.A.E.-based MT Riah.

The Panamanian-flagged tanker stopped transmitting its location early Sunday near Qeshm Island, according to data on the tracking site Maritime Traffic. However, it often did so over the past two years when nearing Iranian waters, other tracking data shows.

U.S. Central Command, which oversees American military operations in the Middle East, declined to comment.

'Very dangerous environment'

It was not immediately clear whether the seizure was a straightforward attempt by Iran to curb oil smuggling or also an effort to assert its authority in the strait and send a message to its rivals in the region. The U.A.E. has long lobbied for tougher U.S. policy toward Iran, though more recently it has called for de-escalation.

Zarif, Iran's foreign minister, said the seized vessel was at best a "small tanker" and that Iranian forces are cracking down on fuel smuggling daily.

"We live in a very dangerous environment. The United States has pushed itself and the rest of the world into probably the brink of an abyss," he told reporters at the United Nations in New York. Zarif accused the Trump administration of "trying to starve our people" and "deplete our treasury" through sanctions.

Iran's Foreign Minister Mohammad Javad Zarif said in New York that the Iranian forces were cracking down on fuel smuggling, and continued to hit back at sanctions applied by the Trump administration. (Richard Drew/The Associated Press)

Iranian media reported earlier this month that some eight million litres of government-subsidized Iranian fuel are smuggled daily through Iran's borders to other countries where prices are much higher.

Analysts at the Israeli-based maritime risk analytics company Windward said the Riah has been at sea for the past two years and has a pattern of turning off its location transmitters for days at a time, particularly when entering Iranian waters.

The firm said data suggests that for more than two years that the 58-metre Riah had been clandestinely receiving fuel from an unknown source off the U.A.E. coast and delivering it to other tankers, which then take it to Yemen and Somalia.

No distress calls were made from the Riah, and no ship owner reported a missing vessel.

U.A.E. disavows connection

The ship's registered owner, Dubai-based Prime Tankers LLC, told The Associated Press it had sold the vessel to another company, Mouj Al-Bahar. A man who answered a telephone number registered to the company told the AP it didn't own any ships.

Officials in the U.A.E. said the ship was neither U.A.E.-owned nor operated and carried no Emirati personnel.

In past weeks, the Persian Gulf region has seen six attacks on oil tankers that the U.S. has blamed on Iran, the downing of a U.S. surveillance drone by Iranian forces and a tense encounter between Iran's Guard and the British navy. Iran has denied involvement in the attacks or the British naval encounter.

The Persian Gulf region has seen six attacks recently on oil tankers that the U.S. has blamed on Iran, the downing of a U.S. surveillance drone by Iranian forces and a tense encounter between Iran's Guard and the British navy. (CBC)

The U.S. has also sent thousands of additional troops and increased its security presence in the region.

Meanwhile, Iran has begun increasing uranium production and enrichment beyond the limits of the 2015 accord in a bid to pressure Europe to find ways around U.S. sanctions.

On Thursday, Iranian President Hassan Rouhani, in a phone conversation with French President Emmanuel Macron, urged European signatories of the deal to speed up their efforts to stop U.S. pressure, his website reported. He said efforts to stop Iran's nuclear activities "are not acceptable under any circumstance."