The Trump administration slapped new sanctions on Iran on Friday, accusing it of keeping top nuclear scientists together as a team so they can forge ahead building nuclear weapons in the future.

The sanctions targeted 14 individuals and 17 companies connected to Iran’s Organization of Defensive Innovation of Research, which is known by its Persian acronym SPND. The Treasury Department said many had worked in the early 2000s on the Amad plan, an early nuclear weapons program, and continue to carry out research and development on dual-use technology that can be employed for energy and medical purposes, as well as potentially to build nuclear weapons.

“The intellectual firepower behind the Amad program very much continues to exist in Iran,” said a senior administration official, speaking on the condition of anonymity under ground rules for briefing reporters. “We are making them radioactive internationally.”

Though the clandestine Amad program was halted in late 2003, many of its records came to light after Israeli Mossad agents broke into a nuclear weapons archive in Tehran and stole a half ton of documents related to building nuclear warheads. Israeli Prime Minister Benjamin Netanyahu announced the caper last April, and said it was another reason President Trump should walk away from the Iran nuclear deal. Trump announced the United States would abandon the agreement the following month.

A second administration official, also speaking to reporters under ground rules of anonymity, said some of the names on Friday’s list were taken from the stash of purloined documents.

Though none of people or groups designated are household names in the United States, they include researchers on radiation, physics and explosives. The administration officials acknowledged that they are not known to be currently involved in building nuclear weapons but called it “gravely concerning” that Iran is keeping together a team of experts with what one U.S. official called the “type of expertise it takes to develop a nuclear program.”

“This is not a run of the mill defense organization,” the official said. “This is a nuclear weapons program waiting to be restarted.”

The sanctions will make it difficult for the targeted individuals to travel abroad for business or personal reasons. They will be restricted from attending international conferences or conducting research and foreign universities. Administration officials said they hope it will discourage young Iranian scientists from going to work for the SPND.

“The message is, don’t do this,” the official said “It’s not a wise thing to be involved in.”

The sanctions were announced as Secretary of State Mike Pompeo was in Lebanon where he is warning officials to limit the influence of Hezbollah, an Iranian-backed group that is part of the Lebanese government but the United States has designated as a terrorist group.