Iran’s leaders Tuesday warned the United States of serious repercussions after it designated the elite Revolutionary Guard Corps a terrorist organization.

President Trump on Monday announced the decision against the Revolutionary Guard, Iran’s most potent military force, describing the move as a way to “expand the scope and scale of our maximum pressure on the Iranian regime.”

The decision would allow the Trump administration to seek criminal penalties against elements of the Guard, one of the most revered institutions in Iran.

The Revolutionary Guard was established in 1979 to protect the Islamic revolution that had just overthrown the country’s long-ruling monarchy.

Iran’s often-bickering leaders have presented a united front in the face of the U.S. move. On Tuesday, lawmakers in parliament wore olive-green fatigues to demonstrate solidarity with the Guard and opened the session with chants of “Death to America.”

President Hassan Rouhani called the U.S. move a “mistake” and said it would only boost the organization’s popularity, at home and abroad. “You thought that if you speak against [the Guard], divisions would arise, or you could reduce its popularity,” Rouhani said, according to the Mehr News Agency.

He spoke at an event marking National Nuclear Day, during which he also warned that U.S. efforts would not hinder Iran’s “scientific progress.” Iran’s nuclear program, which it says is intended solely for peaceful purposes and not for building weapons, has long been of great international concern.

Last year, Trump withdrew the United States from a nuclear deal that Iran struck with world powers in 2015. The pact limited Iran’s nuclear energy program in exchange for widespread sanctions relief.

On Tuesday, Rouhani announced the installation of new centrifuges at the Natanz facility in Isfahan province.

The move is not a violation of the nuclear accord, to which Iran is still a party. It allows for the limited production and testing of advanced centrifuges but without using them to enrich uranium.

But Rouhani signaled Tuesday that Iran may be willing to push the limits.

“If you continue to walk down this road, you will see IR-8 centrifuges in the future,” he said, referring to a more advanced, high-capacity device. “Our patience has a threshold.”

Iran’s supreme leader, Ayatollah Ali Khamenei, held his own event, speaking to members of the Guard and their families, and lauding their role in “defending the country and the revolution.”

He denounced the U.S. decision, saying such “plots” will come back to haunt Trump and his administration, according to a transcript of the remarks posted on Khamenei’s website.

Deputy Foreign Minister Abbas Araghchi, meanwhile, raised the specter of problems in the Persian Gulf, where elements of the Iranian and U.S. navies often confront each other. The waterway carries 20 percent of the world’s oil shipments.

“New incidents may happen,” he said, according to the official Islamic Republic News Agency.