Donald Trump is expected to block all refugees from Syria and six other Middle Eastern and African countries on Wednesday.

Religious minorities escaping persecution will escape the ban which will last for several months, it is thought, until more aggressive vetting is in place.  

Executive ordes expected to be signed on Wednesday will block visas being issued to anyone from Syria, Iraq, Iran, Libya, Somalia, Sudan and Yemen, said aides and immigration experts close to the White House, according to Reuters.

His priority is expected to be plans for a wall along the border with Mexico.

The sources say the first of the orders will be signed on Wednesday. With Trump considering measures to tighten border security, he could turn his attention to the refugee issue later this week.

Stephen Legomsky, who was chief counsel at US Citizenship and Immigration Services in the Obama administration, said the president had the authority to limit refugee admissions and the issuing of visas to specific countries if the administration determined it was in the public's interest.

"From a legal standpoint, it would be exactly within his legal rights," said Legomsky, a professor at Washington University School of Law in St. Louis. "But from a policy standpoint, it would be terrible idea because there is such an urgent humanitarian need right now for refugees."

The Republican president, who took office last Friday, was expected to sign the first of the orders at the Department of Homeland Security, whose responsibilities include immigration and border security.

On the campaign trail, Trump initially proposed a temporary ban on Muslims entering the United States, which he said would protect Americans from jihadist attacks.

Both Trump and his nominee for attorney general, Senator Jeff Sessions, have since said they would focus the restrictions on countries whose migrants could pose a threat, rather than a ban on those of a specific religion.

Many Trump supporters decried former President Barack Obama's decision to increase the number of Syrian refugees admitted to the United States over fears that those fleeing the country's civil war would carry out attacks.

Detractors could launch legal challenges if all the countries subject to the ban are Muslim-majority nations, said immigration expert Hiroshi Motomura at UCLA School of Law.

Legal arguments could claim the executive orders discriminate against a particular religion, which would be unconstitutional, he said.

"His comments during the campaign and a number of people on his team focused very much on religion as the target," Motomura said.

To block entry from the designated countries, Trump is likely to tell the State Department to stop issuing visas to people from those nations, according to sources familiar with the visa process. He could also instruct US Customs and Border Protection to stop any current visa holders from those countries from entering the United States.

Additional reporting by Reuters.