(JTA) — The United States put twin brothers from South Africa who planned attacks on Jewish institutions in their country and on the U.S. Embassy on its terror blacklist.

Brandon-Lee and Tony-Lee Thulsie, 24, were arrested in July 2016 in South Africa and charged with three counts related to terrorism. They had converted to Islam the year before.

The State Department said that because of the threat they pose to U.S. security, the pair had been named Specially Designated Global Terrorists.

“These designations seek to deny Tony-Lee Thulsie and Brandon-Lee Thulsie the resources they need to plan and carry out terrorist attacks,” the State Department said in a statement Tuesday.

“Today’s designations notify the U.S. public and the international community that Tony-Lee Thulsie and Brandon-Lee Thulsie have committed or pose a significant risk of committing acts of terrorism. Terrorism designations expose and isolate entities and individuals, and deny them access to the U.S. financial system. Moreover, designations can assist the law enforcement activities of U.S. agencies and other governments.”

The twins allegedly tried to fly to Syria in April 2015 to join the Islamic State but were stopped after the Hawks, a specialized crime-fighting unit, informed the airline on which they intended to travel. They are subsequently alleged to have “unlawfully and intentionally conspired and attempted to perform acts” that would assist the Islamic State and made themselves available to the terrorist group in order to conduct terrorist activity, the State Department said. The brothers had been under surveillance for about a year before their arrest.

Their arrests reportedly were the first in South Africa relating to alleged membership in the Islamic State.