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 FBI has ramped up its efforts to monitor potential threats to the U.S. from Iran following President Donald Trump’s decision to attack the country’s nuclear facilities, two people briefed on the matter told Reuters on Tuesday.

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.