Initial investigations into the incident by the US NAVCENT (Naval Forces Central Command) found that two limpet mines had been attached to the Kokuka Courageous, WAM news agency reported citing a senior official.
NAVCENT's Explosive Ordnance Disposal Team determined that one mine had caused the explosion while the other, unexploded, had been removed by a boat of the Iranian Revolutionary Guard Corps (IRGC), said Commander Sean Kido, the Commanding Officer of Task Group 56.1 - Explosive Ordnance Dive and Salvage.
Based on the nature of the physical damage to the vessel and materials recovered from the hull, Kido said, NAVCENT had assessed with a high degree of confidence that it was a limpet mine that "bears a striking resemblance" to mines publicly displayed by Iran in military parades and open-source documents.
The damage was not consistent with an external flying object, according to Kido.
He said that the US was continuing the investigations into the incident in cooperation with its allies in the region and that they encourage all parties to respect the free flow of commerce.
Before the press briefing, officials from the Explosive Ordnance Disposal Team showed material evidence collected from the Kokuka Courageous that indicated the presence and removal of a limpet mine.
This evidence included a magnet and composite material, along with aluminium fragments, two holes made by nails and a hand-print on the hull.
The Kokuka Courageous and the other vessel hit during the June 13 attacks, the tanker Front Altair, are currently at anchor off the UAE's East Coast.
The Norwegian-owned Front Altair was hit by three explosions, with no injuries being reported.
( With inputs from IANS )