Iran has threatened to carry out retaliatory attacks in the U.S. in response to the American bombing of three Iranian nuclear facilities on Saturday.

The directive related to counter-terrorism, counterintelligence and cyber security agents who work on issues connected to Iran. FBI field offices in Chicago, Los Angeles, San Francisco, New York and Philadelphia have canceled rotations for agents to work on immigration issues, one of the sources said.

The Federal Bureau of Investigation is moving resources off immigration cases and back to counterterrorism, citing potential threats after the US launched airstrikes on Iranian nuclear sites and helped broker a ceasefire between Iran and Israel following nearly two weeks of fighting.