U.S. President Donald Trump's order banning citizens of 12 countries from entering the United States goes into effect at 12:01 am ET (0401 GMT) on Monday, a move the president promulgated to protect the country from "foreign terrorists."

The countries affected by the latest travel ban are Afghanistan, Myanmar, Chad, Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan and Yemen.

The entry of people from seven other countries - Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela - will be partially restricted.

Trump, a Republican, said the countries subject to the most severe restrictions were determined to harbor a "large-scale presence of terrorists," fail to cooperate on visa security, have an inability to verify travelers' identities, as well as inadequate record-keeping of criminal histories and high rates of visa overstays in the United States.

He cited last Sunday's incident in Boulder, Colorado, in which an Egyptian national tossed a gasoline bomb into a crowd of pro-Israel demonstrators as an example of why the new curbs are needed. But Egypt is not part of the travel ban.

The travel ban forms part of Trump's policy to restrict immigration into the United States and is reminiscent of a similar move in his first term when he barred travellers from seven Muslim-majority nations.

Officials and residents in countries whose citizens will soon be banned expressed dismay and disbelief.

Chad President Mahamat Idriss Deby Itno said he had instructed his government to stop granting visas to U.S. citizens in response to Trump's action.

"Chad has neither planes to offer nor billions of dollars to give, but Chad has its dignity and its pride," he said in a Facebook post, referring to countries such as Qatar, which gifted the U.S. a luxury airplane for Trump's use and promised to invest billions of dollars in the U.S.

Afghans who worked for the U.S. or U.S.-funded projects and were hoping to resettle in the U.S. expressed fear that the travel ban would force them to return to their country, where they could face reprisal from the Taliban.

Democratic U.S. lawmakers also voiced concern about the policies.

"Trump's travel ban on citizens from over 12 countries is draconian and unconstitutional," said U.S. Representative Ro Khanna on social media late on Thursday. "People have a right to seek asylum."