US President Donald Trump is expected to order the building of a wall along the Mexican border on Wednesday, fulfilling one of his key campaign pledges. "Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!" Trump tweeted late Tuesday. The newly inaugurated president is expected to sign executive orders enabling construction of the wall at a town hall meeting of employees at the Department of Homeland Security, the Washington Post reported, citing officials familiar with the matter. Trump will also sign orders cracking down on "sanctuary cities," the Post reported, where local leaders refuse to hand over illegal immigrants for deportation. The orders are set to coincide with a visit by Mexican Foreign Minister Luis Videgaray, who is preparing the ground for President Enrique Pena Nieto's visit next week. It was unclear if Mexico knew in advance of the plans. Trump insisted repeatedly during his campaign that he would build a "big, beautiful wall" along the border to stop illegal immigration and force Mexico to pay for it, despite Mexico's rejection of the plan. Videgaray has previously been burnt by his association with Trump, having organized the then Republican candidate's visit to Mexico during the presidential campaign. The invitation infuriated Mexicans, and Videgaray, then finance minister, was forced to step down, though he was later reinstated to the cabinet following Trump's victory. The New York Times wrote that Trump may also begin targeting legal immigrants this week, including by freezing refugee admissions from Syria and other Muslim-majority countries considered "terror-prone." The move would be in line with Trump's proposal during the campaign to ban Muslim immigrants because of terrorism fears, a plan which alarmed human rights groups. The then candidate also said he would impose "extreme vetting" of immigrants to combat Islamic extremism. An official told the Post that Trump may also suspend the issuing of visas to people from Iraq, Iran, Libya, Somalia, Sudan, Syria and Yemen for 30 days, until new visa procedures have been developed. Other orders expected in the coming days include a review of whether to keep open the Guantanamo Bay detention centre, whether to resume the "black site" secret CIA prison network, and whether to designate the Muslim Brotherhood a terrorist organization, according to the Times.