President Donald Trump is poised to sign executive orders as soon as Wednesday that would limit immigration and the flow of refugees into the United States, restricting access from some predominantly Islamic countries, according to media reports.

Citing congressional aides and immigration experts, Reuters initially reported Tuesday that Trump plans to sign orders Wednesday at the Department of Homeland Security that would restrict travel to the U.S. for refugees and some visa holders from Iraq, Iran, Libya, Somalia, Sudan, Syria and Yemen. The Washington Post, however, reported late Tuesday that the president plans to sign orders related to a border wall and sanctuary cities on Wednesday, then move to immigration- and refugee-related orders later this week.

Trump tweeted late Tuesday that he had a "big day planned on NATIONAL SECURITY tomorrow," and referenced his central campaign promise of building a wall on the U.S. border with Mexico.

Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall! — Donald J. Trump (@realDonaldTrump) January 25, 2017

Trump on the campaign trail also called for a temporary ban on Muslims entering the U.S. and for “extreme vetting” of refugees without providing an explanation for how that would differ from existing stringent government reviews of refugee applications.

Syria has the lowest proportion of Muslim residents among the countries Reuters’ sources cited, at 87 percent, according to the CIA World Fact Book. The others are more than 96 percent Muslim.

Those countries were all included as regional threats in last year’s Worldwide Threat Assessment, a document produced annually by the Office of the Director of National Intelligence that’s considered the intelligence community’s general assessment of threats to U.S. national security. Other predominantly Muslim countries included in the threat report that weren’t specified by Reuters’ sources include Afghanistan, Bangladesh, Egypt and Pakistan. The report also identifies terrorism threats in places like North Africa and Europe.

Homeland Security Secretary John Kelly, a retired Marine four-star general, told members of Congress during his nomination hearing earlier this month that he considered an exclusion based solely on religion to be a mistake and a potential danger in itself.

"I don't think it's ever appropriate to focus on something like religion as the only factor," Kelly said. He recounted his time as a combat commander in Iraq when U.S. forces had to win over the trust of religious leaders.

"Our success in Iraq, certainly my time in Iraq, was because I outreached with people across the spectrum of society, all of whom were Muslim," Kelly said. "We convinced them we were there for good, not evil, that we were there to protect them."