An armored law enforcement vehicle is seen in the area where a man has reportedly taken people hostage at a synagogue during services that were being streamed live, in Colleyville, Texas, U.S. January 15, 2022. REUTERS/Shelby Tauber

The United States faces heightened threats from extremist groups domestic and foreign, underscored by last month’s hostage standoff crisis in a Texas synagogue and bomb threats at many historically Black colleges and universities, a US government agency said on Monday.

The warning comes after some schools across the United States cancelled classes and issued shelter-in-place orders last week. Investigators ultimately failed to turn up any explosives.

“Threats directed at Historically Black Colleges and Universities (HBCUs) and other colleges and universities, Jewish facilities, and churches cause concern and may inspire extremist threat actors to mobilize to violence,” the Homeland Security Department said in a bulletin.

Last month, British-born gunman Malik Faisal Akram took four people hostage at Congregation Beth Israel in Colleyville, Texas, including its rabbi, Charlie Cytron-Walker. He brandished a gun and held them hostage for 10 hours. The standoff ended in gunfire, with all four hostages released unharmed and the suspect dead.

“Supporters of foreign terrorist organizations have encouraged copycat attacks following the January 15, 2022 attack on a synagogue in Colleyville, Texas,” the federal agency added.

The US intelligence community warned months ago of a threat that racially motivated violent extremists, such as white supremacists, would seek to carry out mass-casualty attacks on civilians.

The United States remains in a heightened threat environment, the department said on Monday.

“Foreign terrorists remain intent on targeting the United States and US persons, and may seek to capitalize on the evolving security environment overseas to plot attacks.”

The agency also warned that the Islamic State or its affiliates may issue public calls for retaliation due to a US special forces raid in Syria last week that led to the death of the group’s leader, Abu Ibrahim al-Hashimi al-Quraishi.