The US military has released more photographs to support its claims that Iran was responsible for attacks on commercial tankers in the Gulf of Oman last week, as the Trump administration reportedly prepared to send more troops to the region.

One of the new pictures appeared to show in colour and sharper focus an incident which had previously been presented in a grainy black and white video – a patrol boat with black-uniformed sailors alongside one of the tankers, the Kokuka Courageous.

The acting US defense secretary, Patrick Shanahan, announced on Monday the deployment of about 1,000 additional troops to the Middle East for what he said were “defensive purposes”, citing concerns about a threat from Iran.

“The recent Iranian attacks validate the reliable, credible intelligence we have received on hostile behavior by Iranian forces and their proxy groups that threaten United States personnel and interests across the region,” Shanahan said in a statement.

On Tuesday, the secretary of state, Mike Pompeo, is also due to visit the Florida headquarters of US Central Command (in charge of all operations in the Middle East) and US special forces.

It is unusual for a secretary of state to visit military headquarters, especially as the acting defence secretary is reported to be staying in Washington. Pompeo has taken the lead role in the administration’s campaign of “maximum pressure” on Iran, since the US withdrawal from a multilateral nuclear deal in May last year.

A statement accompanying the images released on Monday said the incident was filmed from a US helicopter and occurred after blasts had hobbled the two ships on 13 June. The crew of the Kokuka Courageous had spotted an unexploded mine on the hull and abandoned ship.

“Later that day, an Islamic Revolutionary Guard Corps (IRGC) Gashti Class patrol boat approached Kokuka Courageous and was observed and recorded by a US navy MH-60R helicopter removing the unexploded limpet mine from Kokuka Courageous,” said the statement issued by US Central Command.

“Iran is responsible for the attack based on video evidence and the resources and proficiency needed to quickly remove the unexploded limpet mine.”

A handout photo made available by the US Department of Defense (DoD) shows the aluminum and green composite material left behind following removal of an unexploded limpet mine used in an attack on the starboard side of motor vessel M/T Kokuka Courageous. Photograph: Us Department Of Defense Handout/EPA

More evidence incriminating Iran in the 13 June tanker attacks in the Gulf of Oman, according to the US. Photograph: -/AFP/Getty Images

One of the images is said to show the remnant of a limpet mine that had been removed – a small jagged piece of green metal, as well as holes made by nails used to hold the mine in place.

The statement does not make any claim on why the Iranians removed the mine, for example in an attempt to remove evidence.

The US has not presented any evidence of mines being attached, and the head of the company operating the Kokuka Courageous, Yukata Katada, has said that the crew had reported that the ship was attacked by a “flying object”.