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 U.S. Navy explosives expert said Wednesday, stopping short of directly blaming Tehran for the assault. The comments by Cmdr. Sean Kido came as the Navy showed reporters pieces of debris and a magnet they said Iran's Revolutionary Guard left behind when they spirited away an unexploded limpet mine after the June 13 attack in the Gulf of Oman.

Kido showed the journalists, including CBS News correspondent Charlie D'Agata, fragments from one of the exploded weapons the U.S. says were used in the attack, in addition to the magnet left affixed to the Japanese ship.

D'Agata said the information was clearly meant to stack up the case against Iran. The Trump administration has insisted Iran was to blame since not long after the attacks last week, and it has steadily ratcheted up that casting of blame and tried to convince allies around the world to point the finger at Tehran, too.

In this handout photo provided by the U.S. Department of Defense, the aluminum and green composite material left behind following removal of an unexploded limpet mine used in an attack on the starboard side of motor vessel M/T Kokuka Courageous is seen on June 14, 2019 in the Gulf of Oman. Getty

In the media briefing in the Gulf on Wednesday, however, D'Agata said all the Navy would confirm was that the limpet mines used bear "a striking resemblance" to those made and shown off previously by Iran -- in other words, no smoking gun. D'Agata noted that the limpet mines used in the attacks are prolific weapons, found in many places in the world.

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Nevertheless, the Navy 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 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."

The 5th Fleet officials also said investigators had recovered fingerprints and a hand print from the Japanese tanker, and D'Agata said they made it clear more details could be released in the coming days.

A picture taken during a guided tour by the US Navy (NAVCENT) to show damage to the Japanese oil tanker Kokuka Courageous off the port of the Gulf emirate of Fujairah, June 19, 2019. Getty

The Navy officials said it was hard to pry one of the magnets used to adhere a limpet mine off of a ship's hull. D'Agata said it took a couple U.S. service members with a crowbar to pry just the single leftover magnet off the Kokuka. The Navy officials said six of the magnets -- each about the size of a softball -- would be used to hold a limpet mine in place on a vessel.

Thus far, German and British officials, along with Iran's arch-rival Saudi Arabia, have backed the U.S. in blaming Iran, or at least saying the evidence suggesting Iranian culpability is strong.

A flat denial

Iran has consistently and completely denied any role in the attacks on tankers near the vital shipping channel of the Strait of Hormuz -- both the recent ones on the two ships in the Gulf of Oman and similar attacks on four tankers last month off the United Arab Emirates port of Fujairah.

"Accusations levelled against Iran's armed forces and the published film with regards to the incident (that) happened to the vessels ... are unsubstantiated and we categorically reject these accusations," Iran's semi-official IRNA news agency quoted Defence Minister Brigadier-General Amir Hatami as saying.

Mounting tension

The attack on the oil tankers came against the backdrop of heightened tensions between the U.S. and Iran that take root in President Donald Trump's decision to withdraw from Tehran's nuclear deal with world powers a year ago.

American officials believe Iran may well be the driving force behind a series of other smaller-scale attacks in the Middle East in recent weeks, including on Saudi oil pipelines and U.S. and allied bases in Iraq.

There was no claim of responsibility, and no culpability assigned immediately for a rocket that hit an oil-drilling site in Iraq's southern Basra province early on Wednesday. The rocket struck inside a compound housing energy giant Exxon Mobil and other foreign oil companies and wounding three local workers, one seriously, Iraqi officials said.

U.S. military officials told CBS News senior national security correspondent David Martin they did not yet "have a good feel" for who was behind the rocket attack.

In recent weeks, the U.S. has sped an aircraft carrier to the Mideast and deployed additional troops to the tens of thousands already here. All this has raised fears that a miscalculation or further rise in tensions could push the U.S. and Iran into an open conflict, some 40 years after Tehran's Islamic Revolution.

Crumbling nuclear deal

Since President Trump pulled the U.S. out of the deal, Iran has threatened to stop adhering to the limits on its nuclear program. It recently 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.

If Iran makes the determination that Europe is not going to risk violating U.S. sanctions to keep doing business with Tehran, it has said it will ramp up uranium enrichment.

An expert told CBS News that Iran could produce enough enriched uranium to be officially in violation of the nuclear deal's terms within days.

That move would likely see the United Nations Security Council petitioned by the U.S. to reinstate broad international sanctions against Iran that were lifted under the terms of the 2015 deal.