By Lesley Wroughton

WASHINGTON (Reuters) – U.S. President Donald Trump on Monday designated Iran’s elite Islamic Revolutionary Guard Corps a foreign terrorist organization, an unprecedented step that raises tension in the Middle East.

Iran has warned it will take reciprocal action against Washington for its move against the Guards, the country’s most powerful security organization.

It is the first time the United States has formally labeled another country’s military a terrorist group.

“The IRGC is the Iranian government’s primary means of directing and implementing its global terrorist campaign,” Trump said in a statement.

The designation “makes crystal clear the risks of conducting business with, or providing support to, the IRGC,” Trump said. “If you are doing business with the IRGC, you will be bankrolling terrorism.” 

Critics have warned that the move could open U.S. military and intelligence officials to similar actions by unfriendly governments. The United States has already blacklisted dozens of entities and people for affiliations with the IRGC, but not the organization as a whole.

Secretary of State Mike Pompeo, a strident critic of Iran, has pushed for the change in U.S. policy as part of the Trump administration’s tough posture toward Tehran. Pompeo told a news conference the designation will take effect in one week.

The announcement comes shortly before the first anniversary of Trump’s decision to pull out of a 2015 nuclear deal with Tehran and to reimpose sanctions that had crippled Iran’s economy.

After reports of the designation emerged late on Friday, Iran warned it will take reciprocal action.

“We will answer any action taken against this force with a reciprocal action,” a statement issued by 255 out of the 290 Iranian lawmakers said, according to IRNA.

Set up after the 1979 Islamic Revolution to protect the Shi’ite clerical ruling system, the IRGC is Iran’s most powerful security organization. It has control over large sectors of the Iranian economy and has a huge influence in its political system.

The IRGC is in charge of Iran’s ballistic missiles and nuclear programs. Tehran has warned that it has missiles with a range of up to 2,000 km (1,242 miles), putting Israel and U.S. military bases in the region within reach.

The United States has already blacklisted dozens of entities and people for affiliations with the IRGC, but the organization as a whole is not.

In 2007, the U.S. Treasury designated the IRGC’s Quds Force, its unit in charge of operations abroad, “for its support of terrorism,” and has described it as Iran’s “primary arm for executing its policy of supporting terrorist and insurgent groups.”

(Reporting by Lesley Wroughton; Writing by Doina Chiacu, Editing by Alistair Bell)