Explosive experts from US Navy say mine used in the attack on an oil tanker in the Gulf of Oman bears a "striking resemblance" to Iranian mines. Iran has denied involvement.
The limpet mines used to attack a Japanese-owned oil tanker near the Strait of Hormuz last week bore "a striking resemblance" to similar mines displayed by Iran, a US Navy explosives expert said on Wednesday, stopping short of directly blaming Tehran for the assault.
Iran has denied being involved in the attack last Thursday that hit the Japanese tanker Kokuka Courageous and also the Norwegian-owned Front Altair.
The comments by Commander Sean Kido came as the Navy showed reporters pieces of debris and a magnet they say Iran's Revolutionary Guard left behind when they spirited away an unexploded limpet mine after the June 13 attack in the Gulf of Oman. Iran has also not acknowledged taking the mine.
Kido also stressed that the damage done to the Kokuka Courageous was "not consistent with an external flying object hitting the ship," despite the ship's owner blaming "flying objects" for the damage in the attack.
Meanwhile, a rocket hit an oil-drilling site in Iraq's southern Basra province early on Wednesday, striking inside a compound housing energy giant Exxon Mobil and other foreign oil companies and wounding three local workers, one seriously, Iraqi officials said.
The attack on the oil tankers came against the backdrop of heightened tensions between the US and Iran that take root in President Donald Trump's decision to withdraw from Tehran's nuclear deal with world powers a year ago.
Iran recently has quadrupled its production of low-enriched uranium and threatened to boost its enrichment closer to weapons-grade levels, trying to pressure Europe for new terms to the 2015 deal.
In recent weeks, the US has sped an aircraft carrier to the Mideast and deployed additional troops to the tens of thousands already here.
Mysterious attacks also have targeted oil tankers as Iranian-allied Houthi rebels launched bomb-laden drones into Saudi Arabia.
All this has raised fears that a miscalculation or further rise in tensions could push the US and Iran into an open conflict, some 40 years after the Iranian Revolution.
Limpet mine found
The US Navy briefed foreign journalists on Wednesday at a 5th Fleet base near Fujairah, an Emirati port city some 210 kilometres (130 miles) northeast of the capital, Abu Dhabi. There, they showed journalists debris recovered from the Kokuka Courageous, which they described as including aluminium and composite metals.
They also showed a magnet they described as being left behind by the Revolutionary Guard — one of six apparently used to stick the unexploded limpet mine to the ship's hull. Sailors said it took two of them and a crowbar to pry it off the ship.
Those pieces put together have US sailors suspecting the limpet mine came from Iran.
They showed a picture previously shared among weapons experts of a limpet mine on display in Iran, which they said resembled the one they suspected was used on the ship.
That picture showed a conical mine, some 42 kilogrammes (90 pounds) in weight, on display with a sign next to it identifying it as being produced by a research company affiliated with the Revolutionary Guard.
"The limpet mine that was used does bear a striking resemblance to that which has been publicly displayed in Iranian military parades," Kido said. "There are distinguishing features."
Kido declined to elaborate. Iran's mission to the UN declined to comment, referring reporters instead to remarks by Iranian Defence Minister General Amir Hatami, who said allegations about Tehran's involvement in the tanker attacks were unfair accusations and "totally a lie" meant to tarnish Iran's image.
According to the semi-official Fars news agency, Hatami questioned the authenticity of a grainy video released by the US following the attack and purporting to show Iranian Revolutionary Guard forces removing an unexploded limpet mine from one of the tankers.
"The date and the location shown in the footage have not been authenticated," he said. The Americans "can show any footage ... but it cannot be used as evidence."
The mines were placed above the vessel's water line. One exploded, punching through the double-hulled ship and sparking a brief fire. The placement of the mines on the vessel makes it "not appear that the intention was to sink the vessel," Kido said.
"The damage we observed is consistent with a limpet mine attack; it is not consistent with an external flying object hitting the ship," Kido said.
Authorities also recovered a handprint and fingerprints, he said. "We recovered biometric information ... which can be used to build a criminal case to hold the individuals responsible accountable." He did not offer more details.
The second vessel involved in the attack, the Norwegian-owned Front Altair, caught fire and sent black smoke up into the air that was visible from space by satellites. Kido did not explain why the US had no immediate evidence from that vessel. Both are now anchored off the eastern coast of the United Arab Emirates.
He also declined to discuss an earlier, May 12 attack on four oil tankers off the coast of Fujairah near the US base, which America similarly blames on an Iranian limpet mine attack. Analysts also believe those attacks came from limpet mines.