US President Donald Trump unleashed a wave of alarm yesterday with his order to temporarily halt all refugee arrivals and impose tough controls on travellers from seven Muslim countries, including war-wracked Syria, to give preference to religious minorities.

Making good on one of his most controversial campaign promises, and to the horror of human rights groups, Trump said the goal is to screen out “radical Islamic terrorists” and that priority for admission would be given to Christians.

“This is big stuff,” he declared at the Pentagon, after signing an executive order on Friday entitled “Protection of the nation from foreign terrorist entry into the United States”.

The countries impacted are Iran, Iraq, Syria, Sudan, Libya, Yemen and Somalia, according to a White House official.

“I hereby proclaim that the entry of nationals of Syria as refugees is detrimental to the interests of the United States and thus suspend any such entry,” the order signed by Trump reads.

The total number of refugees admitted into the United States would also be capped during the 2017 fiscal year at 50,000, down more than half from the current level of 110,000, writes CNN.

“I am establishing new vetting measures to keep radical Islamic terrorists out of the United States of America,” Trump said during the signing after the swearing-in of Defence Secretary James Mattis. “We don’t want them here.”

He added, “We want to ensure that we are not admitting into our country the very threats our soldiers are fighting overseas. We only want to admit those into our country who will support our country and love deeply our people.”

Trump’s decree suspends the entire US refugee resettlement programme for at least 120 days while tough vetting rules are established.

These new protocols will “ensure that those approved for refugee admission do not pose a threat to the security and welfare of the United States.”

In addition, it specifically bars Syrian refugees from the United States indefinitely, or until the president himself decides that they no longer pose a threat.

Meanwhile, no visas will be issued for 90 days to migrants or visitors from the seven countries: Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen, reports AFP.

In reaction to the order, the United Nations yesterday urged the US to continue its “strong leadership role and long tradition of protecting those fleeing conflict and persecution.”

In a joint statement the UN refugee agency, UNHCR, and the International Organisation for Migration said they believed “refugees should receive equal treatment for protection and assistance, and opportunities for resettlement, regardless of their religion, nationality or race.”

France and Germany are “concerned” over a number of decisions by Trump, particularly his move to restrict refugee arrivals, French Foreign Minister Jean-Marc Ayrault said yesterday.

“Welcoming refugees who are fleeing war is part of our duty,” he said following a meeting with his new German counterpart, Sigmar Gabriel.

Thousands of leading academics, alarmed by an executive order signed by Trump on Friday afternoon instituting “extreme vetting” of refugees, have signed onto a petition denouncing his action.

By Friday evening, 11 Nobel laureates and thousands of other academics — many well-known scholars, including Fields medalists, John Bates Clark medalists, members of the National Academy of Sciences and at least one MacArthur Fellow — had signed on. By early yesterday, a 12th Nobel laureate had joined the list.

They were getting about 10 emails a minute, and 15 to 20 volunteers were working to add signatures, an organiser of the effort said Friday evening, according to Washington Post.

Students are horrified at the prospect of not being able to get back to their US universities if they return to their home country, said Emery Berger, a professor in the College of Information and Computer Sciences at the University of Massachusetts Amherst.

“I’m sure it will send really promising star students across the border to Canada or elsewhere,” Berger said. The order comes just as many US universities are offering admission to overseas students for the next academic year. He said an administrator told him Friday to get admissions offers to top Iranian students “yesterday.”

A spokesman for the European Commission said it had “no comment to make” on Trump’s move.

But he recalled “comments made several times by” European Commission President Jean-Claude Juncker, “that Europe is and remains open to all those who flee armed conflicts and terror, whatever their religion.”

US President Donald Trump signs an executive order alongside US Defense Secretary James Mattis and US Vice President Mike Pence at the Pentagon in Washington, DC, on Friday. Trump signed a sweeping new executive order Friday to suspend refugee arrivals and impose tough controls on travelers from seven Muslim countries. Photo: AF

In an interview with the Christian Broadcasting Network earlier Friday, Trump was asked whether he would prioritise persecuted Christians in the Middle East for admission as refugees, and he replied, “Yes.”

“They’ve been horribly treated,” he said. “Do you know if you were a Christian in Syria it was impossible, at least very tough, to get into the United States? If you were a Muslim you could come in, but if you were a Christian it was almost impossible. And the reason that was so unfair — everybody was persecuted, in all fairness — but they were chopping off the heads of everybody, but more so the Christians. And I thought it was very, very unfair.

“So we are going to help them.”

Since the beginning of the Syrian civil war and the rise of the Islamic State, many more Muslims than Christians have been killed or displaced because of the violence. A 2015 Washington Post poll found that 78 percent of Americans favoured equal consideration for refugees regardless of religion.

The order also included a new policy that states and localities should have a say in determining whether refugees can resettle there. It calls for the secretary of homeland security to propose a way to make their involvement routine.

Governors and mayors, mostly Republicans, have objected to refugees, once they are admitted to the country, being resettled in their jurisdictions, often in small and medium-size cities where the cost of living is lower than it is in big coastal cities.

The downsizing of the refugee programme, which had grown under the Obama administration, fulfils Trump’s campaign pledge to start the “extreme vetting” of immigrants and refugees, even though the United States already conducts the most rigorous and drawn-out screening process in the world.

Syrians are subject to special attention because the Islamic State controls significant amounts of territory in their country. An estimated 11 million Syrians have fled their homes since the outbreak of fighting in 2011, with almost 5 million registered as refugees and more than 6 million internally displaced.

US vetting has changed significantly since the refugee programme was suspended for several months after the attacks of Sept 11, 2001.

After applicants register with the UN High Commissioner for Refugees, that agency refers some of the most vulnerable to the United States. They include single mothers and their children, victims of violence and people with severe medical conditions requiring sophisticated treatment. Last year, the UNHCR referred more than 34,000 applicants, up from 16,000 in 2015 and 10,000 the year before that.

Syrians being considered for resettlement in the United States pass through a complex, multi­tiered background investigation. It involves biometric and database screening, personal interviews to look for inconsistencies in their stories, and security screenings by the National Counterterrorism Centre, the FBI, the Department of Homeland Security and the State Department.

The process typically takes nine months to two years to complete.

In the fiscal year that ended in October, the United States admitted 12,500 Syrian refugees. An additional 3,500 were admitted for resettlement in the last three months of 2016. The overwhelming majority were women and children.

Now, with Trump’s executive order, the flow grinds to an immediate halt. People who have sold their belongings in preparation for an imminent departure may not be allowed to board their flights to the United States. It was not immediately clear what would happen to those refugees already in the air when the order was signed.

Google yesterday recalled travelling staff members to the US after the executive order from Trump. It has told the BBC it is concerned about the order and any measures which could block great talent from the US.

The new restrictions will have a major impact on technology companies that hire skilled staff from all over the world on special H1-B visas.

There have already been reports of “green card” holders, who are allowed to work in the US, being prevented from getting on flights. However, green cards are not specifically mentioned in the executive order.

Refugee advocates slammed the order as cruel, while proponents of tighter immigration controls said it would protect Americans from radical Islamists who might try to sneak into the United States as refugees and launch an attack.

But skeptics of current vetting procedures question how effective they can be for refugees from a war-torn country such as Syria.