WASHINGTON — President Donald Trump’s new ban on travel to the U.S. by citizens from 12 mainly African and Middle Eastern countries is set to take effect today amid escalating tension over the president’s unprecedented campaign of immigration enforcement.

The new ban does not revoke visas previously issued to people from countries on the list, according to guidance issued Friday to all U.S. diplomatic missions.

However, unless an applicant meets narrow criteria for an exemption to the ban, his or her application will be rejected starting today. Travelers with previously issued visas should still be able to enter the U.S. even after the ban takes effect.

The ban was quickly denounced by groups that provide aid and resettlement help to refugees.

“This policy is not about national security — it is about sowing division and vilifying communities that are seeking safety and opportunity in the United States,” said Abby Maxman, president of Oxfam America, a nonprofit international relief organization.

— The Associated Press