The US military has released a video it said showed Iran's Revolutionary Guard removing an unexploded limpet mine from one of the oil tankers targeted near the Strait of Hormuz.
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 on Thursday 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.
Iran has denied being involved in the attack, calling it an "unfounded claim" in the US' "Iranophobic campaign".
However, Iran previously used mines against oil tankers in 1987 and 1988 in the Tanker War, when the US Navy escorted ships through the region.
American officials released images they said show that Iran was involved in an attack on an oil tanker near the entrance to the Persian Gulf on Thursday https://t.co/bFIFSuXiGw pic.twitter.com/iveaDaP3zd
— Bloomberg (@business) June 14, 2019
The black-and-white footage, as well as still photographs released by the US military's Central Command, 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," Capt 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.
The suspected attacks occurred at dawn Thursday about 25 miles 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 Commander Joshua Frey, a 5th Fleet spokesman. He described the ships as being hit in a "reported attack", without elaborating.
Thursday's attack resembled that of an attack in May targeting four oil tankers off the nearby Emirati port of Fujairah.
US officials similarly accused Iran of targeting the ships with limpet mines, which are magnetic and attach to the hulls of a ship. The mines disable, but do not sink, a vessel.