U.S. President Donald Trump on Friday put a four-month hold on allowing refugees into the United States and temporarily barred visitors from Syria and some other Muslim-majority countries, saying the moves would help protect Americans from terrorist attacks.

"I'm establishing new vetting measures to keep radical Islamic terrorists out of the United States of America," Trump said as he signed the order. "We don't want 'em here."

Civil rights groups condemned the measures as discriminatory, and said they would strand refugees in dangerous places and would tarnish the reputation of the United States as a land welcoming of immigrants.

90-day immigration ban

The order, which the L.A. Times has posted on its site, imposes a 90-day ban on all entry to the United States from countries with terrorism concerns. The White House says those countries are Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen — all predominantly Muslim countries.

Some exceptions will be made for people travelling on diplomatic visas.

The order also calls for Homeland Security and the State Department, along with the director of national intelligence, to review what information the government needs to fully vet would-be visitors and come up with a list of countries that don't provide it.

The order says the government will give countries 60 days to start providing the information or citizens from those countries will be barred from travelling to the United States.

Syrian refugees cut off

Trump's order directs the State Department to stop issuing visas to Syrian nationals and halts the processing of Syrian refugees.

That will remain in effect until Trump determines that enough security changes have been made to ensure that would-be terrorists can't exploit weaknesses in the current vetting system.

Refugee program suspended

Trump ordered a four-month suspension to his country's broader refugee program. The suspension is intended to provide time to review how refugees are vetted before they are allowed to resettle in the United States.

Trump's order also cuts the number of refugees the U.S. plans to accept this budget year by more than half, to 50,000 people from around the world.

During the last budget year the U.S. accepted 84,995 refugees, including 12,587 people from Syria. President Barack Obama had set the current refugee limit at 110,000.

Priority for Christians in Syria

The temporary halt to refugee processing does include exceptions for people claiming religious persecution, so long as their religion is a minority faith in their country. That could apply to Christians from Muslim-majority countries.

Earlier on Friday, Trump told the Christian Broadcasting Network that Syrian Christians will be given priority when it comes to applying for refugee status.

Stephen Legomsky, a former chief counsel at U.S. Citizenship and Immigration Services in the Obama administration, said prioritizing Christians could be unconstitutional.

"If they are thinking about an exception for Christians, in almost any other legal context discriminating in favour of one religion and against another religion could violate the constitution," he said.

Blasted as discriminatory

Trump's move was immediately condemned by Democrats, civil rights groups, aid groups and others, even before full details emerged.

"Tears are running down the cheeks of the Statue of Liberty tonight as a grand tradition of America, welcoming immigrants, that has existed since America was founded has been stomped upon," said Senate minority leader Chuck Schumer, a New York Democrat.

"'Extreme vetting' is just a euphemism for discriminating against Muslims," American Civil Liberties Union executive director Anthony Romero said in a statement."

President Trump is closing the door on children, mothers and fathers fleeing violence and war. - Malala Yousafzai , activist

Malala Yousafzai, the Nobel Prize-winning girls' education advocate from Pakistan, issued a statement saying she is "heartbroken" by Trump's decision.

"President Trump is closing the door on children, mothers and fathers fleeing violence and war. I am heartbroken that America is turning its back on a proud history of welcoming refugees and immigrants — the people who helped build your country, ready to work hard in exchange for a fair chance at a new life," she said.

The International Rescue Committee, a humanitarian organization that works with refugees overseas and in the U.S., called the move "harmful and nasty."

"In truth, refugees are fleeing terror — they are not terrorists," the group's president David Miliband said. "And at a time when there are more refugees than ever, America must remain true to its core values. America must remain a beacon of hope."

Canada has taken in 39,671 Syrian refugees since November 2015, according to the federal government. The effort is part of a campaign promise by Prime Minister Justin Trudeau.