U.S. President Donald Trump announced on Thursday his intention to halt immigration from what he referred to as “Third World countries,” following an incident in which an Afghan citizen opened fire on two National Guard soldiers in Washington.

Trump wrote on social media: “I will permanently stop immigration from all Third World countries to allow the American system to fully recover.”

He also threatened to cancel “millions” of applications approved under his predecessor, Joe Biden, and to deport anyone who does not provide what he described as “added value” to the United States.