This image released by the U.S. Department of Defense on Monday, June 17, 2019, and taken from a U.S. Navy helicopter, shows what the Navy says are members of the Islamic Revolutionary Guard Corps Navy removing an unexploded limpet mine from the M/T Kokuka Courageous. (U.S. Department of Defense via AP)

This image released by the U.S. Department of Defense on Monday, June 17, 2019, and taken from a U.S. Navy helicopter, shows what the Navy says are members of the Islamic Revolutionary Guard Corps Navy removing an unexploded limpet mine from the M/T Kokuka Courageous. (U.S. Department of Defense via AP)

WASHINGTON (AP) — In an effort to bolster its public case against Iran, the Pentagon on Monday released new photos that officials said show that members of Tehran’s Revolutionary Guard were responsible for attacks last week on two oil tankers near the Persian Gulf.

The images, many taken from a Navy helicopter, show what the Pentagon said were Iranian forces removing an unexploded mine from the side of the Japanese-owned Kokuka Courageous oil tanker in the Gulf of Oman.

Officials last week said the move appeared to be an attempt to remove forensic evidence from the scene of the attack. But it’s not clear if examination of the mine would have made it definitively clear that the device was planted by the IRGC.

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Other photos show a large hole on the side of the Courageous, above the water line, that officials say appears to have been caused by another similar mine.

The release of the photos came as the U.S. works this week to convince members of Congress and allies that the accusations against Tehran are true. Iran has denied involvement in the tanker attacks and has accused America of promoting an “Iranophobic” campaign. Tehran, however, has repeatedly threatened to close the vital Strait of Hormuz, through which 20% of the world’s oil flows.

Secretary of State Mike Pompeo said he made a number of calls Sunday and Monday to international leaders, trying to convince them that keeping the Strait of Hormuz safe and open is a problem they all must deal with.

Relations between the U.S. and Iran have deteriorated in recent months, as the Trump administration restored crippling sanctions and designated the Revolutionary Guard as a foreign terrorist organization.

That increased pressure preceded a string of attacks that the U.S. has blamed on Iran. In late May, four oil tankers off the coast of the United Arab Emirates were attacked with what appeared to be mines, and there was a rocket attack in Baghdad. Last week, similar attacks were launched against the Courageous and the Norwegian-owned MT Front Altair in the Gulf of Oman.

The U.S. military has also accused Iranian Revolutionary Guard troops of trying but failing to shoot down a U.S. drone to disrupt surveillance of the tankers during the attacks.