U.S. NAVY 5TH FLEET BASE, United Arab Emirates — 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 seen in Iran, a U.S. Navy explosives expert said Wednesday, stopping short of directly blaming Tehran for the assault.

Iran has repeatedly denied being involved in the June 13 attack on the Japanese tanker Kokuka Courageous and the Norwegian-owned Front Altair.

The comments by Cmdr. Sean Kido came as sailors showed reporters pieces of debris and a magnet the Navy says was used to attach an unexploded mine to the hull of the Kokuka Courageous. U.S. authorities say the materials were left behind by Iran’s Revolutionary Guard when they spirited away the unexploded mine after the attack in the Gulf of Oman.

Iran, which previously used mines against oil tankers in the crucial waterway in the 1980s, has also not acknowledged retrieving the mine.

Kido stressed that the damage to the Kokuka Courageous was “not consistent with an external flying object hitting the ship,” as the ship’s owner has contended happened during the attack.

“The damage we observed is consistent with a limpet mine attack,” Kido said.

Meanwhile, rockets struck near an oil-drilling site in Iraq’s southern Basra province early Wednesday, including one that hit inside a compound housing energy giant Exxon Mobil and other foreign oil companies and wounding three local workers, one seriously, Iraqi officials said.

The attacks come against the backdrop of heightened tensions between the U.S. and Iran following President Donald Trump’s decision to withdraw from Tehran’s nuclear deal 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 U.S. has sped an aircraft carrier to the Mideast and deployed additional troops beyond the tens of thousands already in the region. 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 U.S. and Iran into an open conflict, 40 years after Tehran’s Islamic Revolution.

The U.S. Navy briefed foreign journalists Wednesday at a 5th Fleet base near Fujairah, an Emirati port city about 130 miles northeast of the capital, Abu Dhabi. They showed journalists debris recovered from the Kokuka Courageous after the attack, including aluminum and composite metals.

They also displayed a magnet, one of six apparently used to attach the unexploded mine to the ship. Sailors said it took two of them and a crowbar to pry it off the ship.

Limpet mines take their name from a mollusk that clings to rock and have been used by a variety of militaries. The mines can be attached by both magnets and nails. The Kokuka Courageous also bore nail holes near where Iranian forces took the unexploded mine, the sailors said.