The United States has demanded Iran release a vanished foreign oil tanker and crew while claiming to have shot down an Iranian drone in the Gulf.

President Donald Trump said the US Navy destroyed the drone in the Strait of Hormuz on Thursday morning local time after the aircraft threatened the amphibious assault ship USS Boxer, coming within 915m and after being warned several times to “stand down”.

He said the drone incident was the “latest of many provocative and hostile actions by Iran against vessels operating in international waters”.

“The United States reserves the right to defend our personnel, facilities and interests,” he said.

“The drone was immediately destroyed.”

I want to apprise everyone of an incident in the Strait of Hormuz today, involving #USSBoxer, a U.S. Navy amphibious assault ship. The BOXER took defensive action against an Iranian drone…. pic.twitter.com/Zql6nAUGxF

— Donald J. Trump (@realDonaldTrump) July 18, 2019

Iranian Foreign Minister Mohammad Javad Zarif told reporters at the United Nations: “We have no information about losing a drone today.”

The Pentagon said in a statement that the USS Boxer, with an estimated 2000 sailers on board, had taken “defensive action” against the drone as the Boxer was moving into the Strait of Hormuz.

“We do assess it was an Iranian drone,” said Pentagon spokeswoman Commander Rebecca Rebarich.

A file photo of the USS Boxer docked in Hong Kong. Photo: Getty

It comes as Iran claims to have seized an oil tanker which it accuses of attempting to smuggle oil through the vital shipping passage.

Iran’s Revolutionary Guard says it apprehended the vessel, which has yet to be formally identified, for shipping one million litres of fuel from Iranian smugglers to foreign customers, Iran’s state TV has reported.

The US State Department has insisted Iran free the ship and its 12 crew members and stop harassing vessels in and around the vital shipping passage through the Gulf.

The US blames Iran for a series of attacks on shipping since mid-May in the world’s most important oil artery, accusations Tehran rejects.

Earlier, the US issued a statement calling on the missing ship’s release.

“The United States strongly condemns the Islamic Revolutionary Guard Corps Navy’s continued harassment of vessels and interference with safe passage in and around the Strait of Hormuz,” a State Department spokesperson said a statement.

“Iran must cease this illicit activity and release the reportedly seized crew and vessel immediately.”

It was unclear if the impounded ship was the same vessel that Iran says it towed to safety on Sunday when Iran’s Foreign Ministry claimed it sent a distress signal.

An Emirati official has stated the unidentified vessel made no distress call before switching off its tracker.

The latest incident comes a week after the UAE tanker MT Riah disappeared off trackers in Iranian territorial waters and shipping industry sources said they believed it was the same seized tanker.

The last signal received from the vessel was on Sunday when it was in the Strait of Hormuz.

US intelligence officials reportedly suspect that the 58-metre Riah had been forced into Iranian waters by Iran’s naval forces.

Iranian state television had earlier said it was the same ship but a Revolutionary Guards statement did not confirm that.

US Central Command chief General Kenneth McKenzie said Washington was talking to several countries about ensuring freedom of navigation in the Gulf and would work “aggressively” to find a solution to enable free passage.

Washington has beefed up its military presence and the US Fifth Fleet, based in Bahrain, and says Gulf Arab states have stepped up patrols.

Revolutionary Guards commander-in-chief Hossein Salami said Iran had adopted a defensive strategy but warned that “if our enemies make any mistakes …. our strategy can become an offensive one, ” Iranian media reported.

Meanwhile, the US announced it has imposed sanctions on an international network of companies and their agents it said were involved in the procurement of materials for Iran’s nuclear program.

They are the first punitive steps by Washington since Tehran announced earlier this month it would increase its levels of enriched uranium that can be used for bomb fuel.

-with AAP