The U.S. government has halted all immigration applications from 19 countries and temporarily canceled citizenship ceremonies nationwide, citing security and public-safety concerns.

According to The New York Times, the freeze could affect more than 1.5 million people with pending asylum applications and over 50,000 individuals who were granted asylum under the Biden administration.

The New York Post also reports that President Donald Trump is considering expanding the existing travel ban to more than 30 countries.

The new directive follows last week’s attack in Washington, D.C., where Afghan national Rahmanullah Lakanwal was arrested for allegedly killing one National Guard member and injuring another.

The freeze currently applies to citizens of:

Afghanistan, Myanmar, Chad, the Republic of Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan, Yemen, and restrictions also affect Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan, and Venezuela.

The order blocks all immigration-related processing, including a pause on citizenship ceremonies for legal permanent residents from the affected countries, CBS News reports.

USCIS spokesperson Matthew Tragesser said:

“The Trump administration is making every effort to ensure individuals becoming citizens are the best of the best. Citizenship is a privilege, not a right. We will take no chances when the future of our nation is at stake.”

A Department of Homeland Security memo obtained by The Washington Post states that anyone seeking to migrate to the U.S. from the affected nations will undergo fresh, extensive security vetting, including possible re-interviews.

The memo also gives DHS authority to deny applications under a broad definition of “inadmissibility or ineligibility.”