American military officials said Friday that Iran's Revolutionary Guard Corps (IRGC) is directly responsible for attacks on tankers off the United Arab Emirates earlier this month.

The officials said the attacks were part of a “campaign” by the Iranian regime that prompted the U.S. to deploy additional troops to the Middle East.

“The attack against the shipping in Fujairah we attribute it to the IRGC,” said Rear Admiral Michael Gilday, the director of the Joint Staff. He added that the Pentagon attributed limpet mines used in the attack to the IRGC. He declined to describe “the means of delivery” of the mines.

Military experts initially said that the attacks on oil tankers were perpetrated by Iran or its proxies, but didn’t name the exact party responsible.

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The IRGC was formally classified last month as a “foreign terrorist organization” in an effort to put further pressure on Iran.

Secretary of State Mike Pompeo, citing the IRGC's ties to terror plots, said the designation recognizes a "basic reality."

“This designation is a direct response to an outlaw regime and should surprise no one,” he said. “The IRGC masquerades as a legitimate military organization, but none of us should be fooled.”

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Trump said Friday that the U.S. will deploy an additional 1,500 troops to the region amid heightened tensions with Iran that already led to the deployment of additional warships and bombers to the Middle East earlier this month to counter unspecified threats to U.S. interests.

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In addition, all non-essential U.S. staff at the U.S. Embassy and Consulate in Iraq were ordered to leave following a surprise visit by Pompeo.

The top diplomat previously said U.S. intelligence shows that Iranian-backed militia groups moved their rockets near bases housing American personnel.

Trump said the troops would have a "mostly protective" role as part of a build-up that began this month in response to what the U.S said was a threat from Iran without providing details or evidence.

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"We are going to be sending a relatively small number of troops, mostly protective," the president said before setting off on a trip to Japan. "Some very talented people are going to the Middle East right now and we'll see what happens."

The additional forces will also include more manned and unmanned aircraft, a squadron of fighter jets, a Patriot missile battalion and military engineers.

The Associated Press contributed to this report.