The United States has announced plans to lift its ban on refugees from 11 "high-risk" countries, but said those seeking to enter the US would come under much tougher scrutiny than in the past.

Applicants from 11 countries, unnamed but understood to include ten Muslim-majority nations plus North Korea, will face tougher "risk-based" assessments to be accepted.

"It's critically important that we know who is entering the United States," said Homeland Security Secretary Kirstjen Nielsen.

"These additional security measures will make it harder for bad actors to exploit our refugee programme, and they will ensure we take a more risk-based approach to protecting the homeland."

The 11 countries, hit with a ban in October in the Trump administration's revised refugee policy, have not been identified officially.

But refugee groups say they comprise Egypt, Iran, Iraq, Libya, Mali, North Korea, Somalia, South Sudan, Sudan, Syria and Yemen.

Speaking anonymously, a senior administration official told journalists that the policy of enhanced security assessments for the 11 countries was not designed to target Muslims.

"Our admissions have nothing to do with religion," the official said, adding that there is "nothing especially novel" about tougher screening for countries deemed to have a higher level of risk.

US President Donald Trump has pursued a much tougher stance on immigrants and refugees from all countries since becoming president in 2017.

His predecessor Barack Obama set refugee admissions at 110,000 for 2017.

When Mr Trump took office in January last year, he slashed that to 53,000, and it was cut again to a maximum of 45,000 for 2018.

But refugee arrivals this year could come in significantly lower than that, due to the backlog from the 120-day halt and a slowdown in processing because of generally tougher applicant reviews.

DHS would not explain what the tougher vetting measures for the 11 countries would include.

But all applicants are being asked to supply more detailed histories and evidence of their past activities, and many are having to allow access to personal electronics and social media accounts.

The move comes as Mr Trump presses for a sharp turn in overall US immigration policy that critics say will result in a 50% cut in arrivals each year and move admissions away from African, Asian and Muslim countries.