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 and a major component of its economy.
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.
In reaction to the designation, Iranian Foreign Minister Mohammad Javad Zarif accused Israel's supporters of being behind the administration's decision. According to other media reports, he also advised the Iranian regime of retaliating by designating U.S. forces in the region as terrorists.