The limpet mine used in the attack against a Japanese-owned oil tanker last week "bears a striking resemblance" to similar Iranian mines, said a US Navy explosive expert Wednesday.
"The limpet mine that was used in the attack is distinguishable and also strikingly bearing a resemblance to Iranian mines that have already been publicly displayed in Iranian military parades," said Commander Sean Kido, the commanding officer of an explosive ordinance dive and salvage task group in the Naval Forces Central Command (NAVCENT).
He added that damage done to tanker Kokuka Courageous was "not consistent with an external flying object hitting the ship."
That contradicts the ship's owner, which said eyewitnesses aboard saw "flying objects" before the June 13 attack in the Gulf of Oman.
Kido added that Navy investigators have recovered fingerprints and a hand print from the side of the ship after the attack.
Iran has repeatedly denied being involved in the attack.
Defense Minister Brigadier-General Amir Hatami rejected Wednesday the accusations, describing evidence presented by Washington as "unsubstantiated", official news agency IRNA reported.
"Accusations leveled 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," he stated.
Tensions between Tehran and Washington have grown since the US unilaterally quit the multilateral 2015 nuclear deal last year and reimposed sanctions on Iran.
The US has bolstered its military presence in the Middle East and blacklisted Iran's Revolutionary Guards as a terrorist organization.