The United States military on Thursday released a video that it says shows an Iranian navy boat removing an unexploded mine attached to the hull of the Japanese-owned chemical tanker Kokura Courageous, one of two tankers attacked in the Gulf of Oman.

Secretary of State Mike Pompeo on Thursday blamed Iran for attacking the Kokura Courageous and another ship, Norwegian-owned Front Altair, saying the assessment was based on intelligence.

Later Thursday night, US Central Command released the video, which it says shows Iranian sailors removing a mine from the Kokura Courageous’ hull.

In the video, a smaller boat is shown coming up to the side of the Japanese-owned tanker. An individual stands up on the bow of the boat and can be seen removing an object from the tanker's hull. The US says that object is likely an unexploded mine.

The attack comes at a time of high tensions between the US and Iran and could provide more fodder for Iran hawks within the administration, whose recent Iran sabre-rattling has frustrated President Donald Trump.

One of them, national security adviser John Bolton, announced last month that the Pentagon was deploying the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the Middle East in response to a “number of troubling and escalatory indications and warnings” from Iran.

Earlier in the day, four US officials told CNN the US had the images.

The boat made the move even after the destroyer USS Bainbridge, as well as a US drone and P-8 aircraft, had been on the scene for four hours.

US defence officials believe that the Iranians were seeking to recover evidence of their involvement in the attack.

Another of the officials told CNN that multiple Iranian small boats have entered the area where the Bainbridge continues to be on the scene, prompting US Central Command to issue a statement saying, “No interference with USS Bainbridge, or its mission, will be tolerated.”

The two tankers — one carrying oil and the other transporting chemicals — were attacked in international waters near the strategically important Strait of Hormuz.

All crew members were evacuated and were safe, according to the owners of the two ships. Images released by the US Central Command on Thursday showed crew from the USS Bainbridge assisting crew members of the Kokuka Courageous following their rescue.  

“These appeared to be well-planned and coordinated” attacks, the association said. Jonathan Cohen, acting US ambassador to the United Nations, said Thursday that he echoed Pompeo's comments in a private meeting of the UN Security Council, describing the attack as “another example of Iran's destabilizing activities in the region.”

The Iranian mission to the UN rejected the US’ claim. Alireza Miryousefi, a spokesman for the Iranian mission, tweeted a statement saying Iran “categorically rejects the US unfounded claim” that Iran is behind the attacks and “condemns it in the strongest possible terms.”

He added that Iran “expresses concern” over the “suspicious incidents.” And he called it “ironic” that the US, which withdrew from the nuclear deal with Iran, the Joint Comprehensive Plan of Action, is now calling Iran to come back for negotiations and diplomacy.

Following the attack, Iran's foreign minister, Mohammad Javad Zarif, said “suspicious doesn't begin to describe” this latest incident, noting that one of the tankers is Japanese owned and the attack took place as Japanese Prime Minister Shinzo Abe was visiting Iran in an effort to calm tensions between Washington and Tehran.

“Reported attacks on Japan-related tankers occurred while PM was meeting with Ayatollah [Ali Khamenei] for extensive and friendly talks. Suspicious doesn't begin to describe what likely transpired this morning,” Zarif tweeted Thursday.

The incident follows attacks on four oil tankers in the United Arab Emirates’ port of Fujairah in May. Initial findings from an international investigation of the attack last month concluded that a “state actor” was the most likely culprit.

The UAE, Saudi Arabia and Norway told the UN Security Council last week that there are “strong indications that last month's attacks were part of a sophisticated and coordinated operation carried out with significant operational capacity.”