US President Donald Trump has signed an executive order that suspends the country's refugee program for four months and halts the entry of Syrian refugees indefinitely, a move he says is aimed at keeping "radical Islamic terrorists" out of America.

Key points: Processing of Syrian nationals won't continue until vetting system is improved

Processing of Syrian nationals won't continue until vetting system is improved Number of refugees accepted this budget year cut by more than half

Number of refugees accepted this budget year cut by more than half People claiming religious persecution are excluded from processing halt

People claiming religious persecution are excluded from processing halt Immigration from countries with terrorism concerns suspended for 90 days

The order imposes stringent regulations on many potential immigrants, suspends all refugee admissions for four months and authorising "extreme vetting".



"I'm establishing new vetting measures to keep radical Islamic terrorists out of the United States of America. Don't want them here," Mr Trump said.

"We only want to admit those into our country who will support our country and love deeply our people."

The order directs the State Department to stop issuing visas to Syrian nationals and halts the processing of refugees from the war-torn country indefinitely, stating that their entry is "detrimental to the interests of the United States".

The program will be suspended until their admission to the country is "consistent with the national interest".

In addition, America's broader refugee admissions program has been suspended for four months so a review can take place on how refugees are vetted.

All immigration from countries with terrorism concerns has also been suspended for 90 days. It is not clear which countries will be affected, however, a draft order identified Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen — all majority-Muslim countries.

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

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

The temporary halt to refugee processing will eventually give priority to minority religious groups fleeing persecution.

Mr Trump said the exception would help Syrian Christians fleeing the civil war there but legal experts said singling out a particular religion could be challenged as a violation of the US Constitution.

Mr Trump had promised the vetting measure during last year's election campaign, saying it would prevent militants from entering the United States from abroad.

However, civil rights groups have condemned the move as harmful and discriminatory, and aid agencies had urged Mr Trump not to turn his back on refugees.

"President Trump has cloaked what is a discriminatory ban against nationals of Muslim countries under the banner of national security," said Greg Chen of the American Immigration Lawyers Association.

Turnbull 'confident' US will honour refugee deal

Prime Minister Malcolm Turnbull has said he remains confident the United States will honour its refugee resettlement deal, despite Mr Trump's latest executive order.

Prior to Mr Trump taking office a deal was made to resettle refugees on Manus Island and Nauru.

Mr Turnbull says there is a section within the order which states officials can still use their discretion to admit refugees, under pre-existing international arrangements.

"It's quite clear that the administration has set out in the order the ability to deal with existing arrangements, such as the one we have," Mr Turnbull said.

"We are very confident and satisfied that the existing arrangements will continue."

The section Mr Turnbull referred to, section 5E, was missing from the draft executive order released last week.

The ABC understands it was only included in the final version after a direct intervention from Mr Turnbull's office.

Trump orders 'great rebuilding of armed services'

Donald Trump said James Mattis (L) is a man of "total action". ( Reuters: Carlos Barria )

Mr Trump also signed an order for new spending on the US armed forces, which he said was aimed at "rebuilding" defence and includes new planes and ships.

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"I'm signing an executive action to begin a great rebuilding of the armed services of the United States, developing a plan for new planes, new ships, new resources and new tools for our men and women in uniform and I'm very proud to be doing that," he said.

Mr Trump signed the orders after the swearing-in ceremony of Defence Secretary James Mattis.

The President said Mr Mattis has devoted his life to serving the country and was a "man of total action".

"He is a man of honour, a man of devotion and a man of total action. He likes action. He is the right man at the right time and he will do us all very proud," Mr Trump said.

Trump meets May, NATO and torture discussed

Earlier in the day Mr Trump reaffirmed his "unshakable commitment" to NATO when he met with British Prime Minister Theresa May at the White House.

Although Mr Trump had earlier suggested NATO was obsolete, Ms May said the President confirmed he was "100 per cent" behind the alliance.

On the question of lifting sanctions on Russia, a move Britain opposes, Mr Trump said it was "very early to be talking about that".

Sorry, this video has expired Theresa May unequivocal on Russia sanctions but Trump says it's 'very early' to be discussing

Mr Trump was also asked about a more contentious issue: his recent statements that torture "does work" in prying information out of terror suspects.

Giving ground, he said his Defence Secretary's opposition to waterboarding and other enhanced interrogation techniques would override his own belief.

"I happen to feel that it does work. I've been open about that for a long period of time. But I am going with our leaders."

At the joint news conference with Ms May, Mr Trump also said he had a "friendly" call with Mexican President Enrique Pena Nieto earlier in the day but reaffirmed his belief that Mexico has "beat [the US] to a pulp".

During the "constructive and productive" phone call between the leaders, they agreed they would not talk publicly about payment of the border wall Mr Trump wants to build.

ABC/AP/Reuters