US President Donald Trump signed an order Friday to strengthen the vetting of would-be immigrants or refugees and to keep "radical Islamic terrorists out of the United States of America."

Washington (AFP) - US President Donald Trump signed an order Friday to strengthen the vetting of would-be immigrants or refugees and to keep "radical Islamic terrorists out of the United States of America."

At a ceremony at the Pentagon to swear in James Mattis as his secretary of defense, Trump signed a decree entitled: "Protection of the nation from foreign terrorist entry into the United States."

"This is big stuff," he declared, to polite applause from gathered senior military brass.

The White House did not immediately make the wording of the decree public, but a draft text had been leaked to US media earlier in the week and was widely reported on.

According to this unconfirmed order, Trump's decree suspends the entire US refugee resettlement program for at least 120 days while tough new vetting rules are established.

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 30 days to travellers, whether would-be visitors or migrants, from seven mainly-Muslim countries: Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen.