An MQ-9 Reaper remotely piloted drone aircraft performs aerial maneuvers over Creech Air Force Base U.S. Air Force/Senior Airman Cory D. Payne/Handout via REUTERS

The crew of an Iranian boat fired a surface-to-air missile at a US drone just hours before the tanker attack Thursday, CNN reported Friday afternoon.

Before the unmanned aircraft was fired upon, the drone reportedly spotted Iranian vessels closing on the tankers. While this is evidence of Iranian movement prior to the attack, it is unclear if these vessels were involved.

As it did with the tanker attacks last month, the US blamed Iran for the latest attacks. Tehran has denied all responsibility.

Just a few hours before Thursday's attack on two tankers in the Gulf of Oman, the crew of an Iranian boat reportedly fired a missile at a US drone.

The surface-to-air missile missed the MQ-9 Reaper drone, CNN reported Friday, citing a US official who revealed that before the Iranians opened fire the unmanned aerial vehicle spotted Iranian ships closing in on the two tankers.

This report, which INSIDER was not able to immediately verify, adds to the body of evidence produced by the US that Iranian forces were involved in the attack on the tankers.

The US pinned the blame for Thursday's attack on Iran.

"It is the assessment of the U.S. government that Iran is responsible for today's attacks in the Gulf of Oman," Secretary of State Mike Pompeo said. "These attacks are a threat to international peace and security, a blatant assault on the freedom of navigation, and an unacceptable escalation of tension by Iran."

An oil tanker is seen after it was attacked at the Gulf of Oman Reuters

US Central Command later released photos of a suspected unexploded limpet mine attached to the hull one of the targeted tankers. The combatant command also released a video showing the crew of an Iranian patrol boat sailing out and taking the mine.

President Donald Trump doubled down Friday morning, telling Fox & Friends that the attack "has Iran written all over it."

The US also blamed an attack on four tankers off the coast of the United Arab Emirates last month on Iran, with an investigation into the incident concluding that it was highly likely that limpet mines were used against the four vessels.

Tehran has repeatedly denied all allegations, which come amid heightened tensions with the US.

The US began moving additional firepower into the US Central Command area of responsibility last month in response to various unspecified threats from Iran. "We obviously need to make contingency plans should the situation deteriorate," Acting Secretary of Defense Patrick Shanahan said Friday.

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