The US military has released a video it says shows Iran's Revolutionary Guard removing an unexploded limpet mine from one of the oil tankers targeted near the Strait of Hormuz.
They believe it suggests the Islamic Republic sought to remove evidence of its involvement from the scene.
Iran denies being involved, accusing the US instead of waging an 'Iranophobic campaign' against it.
The US Navy rushed to assist the stricken vessels in the Gulf of Oman, off the coast of Iran, including one that was set ablaze yesterday by an explosion.
The ships' operators offered no immediate explanation on who or what caused the damage against the Norwegian-owned MT Front Altair and the Japanese-owned Kokuka Courageous.
Each was loaded with petroleum products, and the Front Altair burned for hours, sending up a column of thick, black smoke.
While Iran has denied being involved in the attack, Tehran previously used mines against oil tankers in 1987 and 1988 in the 'Tanker War,' when the US Navy escorted ships through the region.
The black-and-white footage, as well as still photographs released by the US military's Central Command today, appeared to show the limpet mine on the Kokuka Courageous.
A Revolutionary Guard patrol boat pulled alongside the ship and removed the mine, Central Command spokesman Captain Bill Urban said.
'The US and the international community stand ready to defend our interests, including the freedom of navigation,' Urban said.
'The United States has no interest in engaging in a new conflict in the Middle East. However, we will defend our interests.'
Iran earlier denied involvement via a statement from its mission to the United Nations.
'The US economic war and terrorism against the Iranian people as well as its massive military presence in the region have been and continue to be the main sources of insecurity and instability in the wider Persian Gulf region and the most significant threat to its peace and security,' the statement said.
Meanwhile in Tokyo, the owner of the Kokuka Courageous said its sailors saw 'flying objects' before the attack, suggesting it wasn't damaged by mines.
Company president Yutaka Katada offered no evidence for his claim, which contradicts the US military account.
Katada also said crew members saw an Iranian naval ship nearby, but did not specify whether this was before or after the attacks.
The suspected attacks occurred at dawn yesterday about 40km off the southern coast of Iran.
The Front Altair, loaded with the flammable hydrocarbon mixture naphtha from the United Arab Emirates, radioed for help as it caught fire.
A short time later, the Kokuka Courageous, loaded with methanol from Saudi Arabia and Qatar, also called for help.
The US Navy sent a destroyer, the USS Bainbridge, to assist, said Cmdr. Joshua Frey, a 5th Fleet spokesman. He described the ships as being hit in a 'reported attack,' without elaborating.
US Secretary of State Mike Pompeo told journalists yesterday that the US assessment of Iran's involvement was based in part on intelligence, as well as the expertise needed for the operation.
© AAP 2019