A US warship has destroyed an Iranian drone that came with "threatening distance" in the Strait of Hormuz amid heightened tensions between the two countries.
The incident marked a new escalation between the countries less than one month after Iran downed an American drone and Trump came close to retaliating with a military strike.
Announcing the move during a press conference at the White House, Donald Trump blamed Iran for a "provocative and hostile" action and said the U.S. responded in self-defense.
He called on other countries to condemn what he says are Iran's attempts to disrupt the freedom of navigation and global commerce in the strategic waterway in the Persian Gulf.
Mr Trump said the USS Boxer took defensive action after the drone closed to within 1,000 yards of the warship and ignored multiple calls to stand down.
He said the drone threatened the safety of the American ship and its crew.
"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," Mr Trump said.
The Pentagon also said the incident happened at 10am local time on Thursday in international waters while the Boxer was transiting the waterway to enter the Persian Gulf.
"A fixed wing unmanned aerial system approached Boxer and closed within a threatening range," spokesman Jonathan Hoffman said in a statement.
"The ship took defensive action against the UAS to ensure the safety of the ship and its crew."
It was the latest in a string of moves by the US and Iran that have brought them closer to armed conflict since early May when Washington accused Tehran of threatening US forces and interests in Iraq and in the Gulf.
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
In response, the US accelerated the deployment of an aircraft carrier strike group to the Arabian Sea and deployed four B-52 long-range bombers to the Gulf state of Qatar. It also has deployed additional Patriot air defense missile batteries in the Gulf region since then.
Shortly after Iran shot down a US Navy drone aircraft on June 20, Trump ordered a retaliatory military strike but called it off at the last moment, saying the risk of casualties was disproportionate to the downing by Iran, which did not cost any US lives.
Iran claimed the US drone violated its airspace, which the Pentagon denies.
Iran's foreign minister, Mohammad Javad Zarif, said on Thursday that Iran and the US were only "a few minutes away from a war" after Iran downed the American drone.
He added that "we have no information about losing a drone today."
The latest incident came hours after Iran's state TV reported that the country's paramilitary Revolutionary Guard forces had seized a foreign oil tanker for smuggling fuel out of the country.
Hours later, it released a video showing the vessel as a United Arab Emirates-based ship, the MT Riah, that had vanished in Iranian waters over the weekend.
The footage shows the ship surrounded by Guard vessels and showed the registration number painted on its bridge, matching that of the UAE-based MT Riah.
It said it had been involved in smuggling some 1 million litres (264,000 gallons) of Iranian fuel.
Iran, which had initially withheld the name of the tanker, did not identify the nationalities of the crew but said the tanker was intercepted in south of Iran's Larak Island in the Strait of Hormuz.
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.
Crude prices, which had been falling since last week, ticked higher almost immediately after the announcement.
A US state department spokesman has now urged the Guards to release the tanker, accusing them of "continued harassment of vessels and interference with safe passage in and around the Strait of Hormuz."
They said: "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.
"Iran must cease this illicit activity and release the reportedly seized crew and vessel immediately."