Trump's new travel ban takes effect amid escalating tension over immigration enforcement

President Donald Trump's new ban on travel to the US by citizens from 12 mainly African and Middle Eastern countries is set to take effect Monday amid rising tension over the president's escalating campaign of immigration enforcement.

It also imposes heightened restrictions on people from Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela who are outside the US and don't hold a valid visa.

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

However, unless an applicant meets narrow criteria for an exemption to the ban, his or her application will be rejected starting Monday.

Travelers with previously issued visas should still be able to enter the US even after the ban takes effect.

Many immigration experts say the new ban is designed to beat any court challenge by focusing on the visa application process and appears more carefully crafted than a hastily written executive order during Trump's first term that denied entry to citizens of mainly Muslim countries.

Trump also tied the new ban to a terrorist attack in Boulder, Colorado, saying it underscored the dangers posed by some visitors who overstay visas.

The man charged in the attack is from Egypt, a country that is not on Trump's restricted list. US officials say he overstayed a tourist visa.

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