President Donald Trump has directed the federal agency that oversees legal immigration to the U.S. to conduct a sweeping review of green card holders from what the administration calls countries of concern, the head of U.S. Citizenship and Immigration Services said.

USCIS did not specify which countries it would focus on. The announcement comes a day after a shooting near the White House left two members of the National Guard in critical condition, with authorities identifying the suspect as an Afghan national.