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

The new proclamation, which Trump signed on Wednesday, applies to citizens of Afghanistan, Myanmar, Chad, the Republic of Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan, and Yemen. 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.

Haitian-American Elvanise Louis-Juste, who was at the airport Sunday in Newark, New Jersey, awaiting a flight to her home state of Florida, said many Haitians wanting to come to the US are simply seeking to escape violence and unrest in their country.

“I have family in Haiti, so it’s pretty upsetting to see and hear,” Louis-Juste, 23, said of the travel ban. “I don’t think it’s a good thing. I think it’s very upsetting.”

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.

In a video posted Wednesday on social media, Trump said nationals of countries included in the ban pose “terrorism-related” and “public-safety” risks, as well as risks of overstaying their visas. He also said some of these countries had “deficient” screening and vetting or have historically refused to take back their citizens.

His findings rely extensively on an annual Homeland Security report about tourists, businesspeople, and students who overstay US visas and arrive by air or sea, singling out countries with high percentages of nationals who remain after their visas expired.

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

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.

Venezuela President Nicolás Maduro’s government was among those that condemned the travel ban, characterizing it in a statement as a “stigmatization and criminalization campaign” against Venezuelans.