President Donald Trump on Wednesday ordered construction of a wall along the country's southern border with Mexico to thwart illegal migration, and at the same time he confronted hundreds of U.S. cities that have refused to help federal authorities identify and deport undocumented migrants.
The new president signed the immigration executive orders as he visited the Department of Homeland Security, the federal agency charged with protecting the U.S. border, and he planned to take additional actions in coming days.
The orders served as an exclamation point to one of the major forces behind Trump's lengthy run to a four-year term in the White House: his contention that illegal migrants in the U.S. threaten its security and cost American workers their jobs. At rally after rally during his campaign, his most fervent cheering supporters shouted, "Build that wall!"
Trump told ABC News that construction of the wall would start within months, and he continued to contend that Mexico would pay for it, although Mexico has repeatedly said it will not. Trump said the payment would perhaps be in a "complicated form," signaling it would not be a direct payment from Mexico City to Washington.
WATCH: Trump on American reimbursement for border wall
White House spokesman Sean Spicer said the U.S. would build more detention facilities along the border to house migrants who cross the border and then give them a "one-way ticket back to the country of their origin." He said the Trump administration would end what he called the "dangerous catch-and-release program" border agents have employed, eliciting promises from migrants to appear later in court, which they then have often ignored.
Officials said Trump was also considering a four-month freeze on all refugee admissions, as well as a ban for at least 30 days on entry to the U.S. by anyone from Iraq, Iran, Libya, Syria, Somalia, Sudan and Yemen — all Muslim-majority countries. The ban could include an exception for people who are religious minorities in their country and are facing persecution.
Trump often used his campaign rallies to criticize U.S. admissions of refugees, employing the phrase, "We have no idea who these people are." He also initially proposed a ban on admitting people from Muslim countries, drawing sharp criticism. He later amended his stance to include countries with links to terrorism.
Trump, on his Twitter account Tuesday night, wrote, "Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!"
The president wants a wall along the entire 3,200-kilometer length of the U.S.-Mexico border. Currently, there is a barrier along only some of the border, although U.S. agents patrol it in vehicles and monitor it with unmanned drones, infrared video and other means.
Trump frequently has vowed that Mexico will pay for the wall, saying Congress will initially authorize the U.S. government to pick up the cost — possibly $10 billion or more — and be reimbursed later by the Mexican government.
Mexico has repeatedly stated it will not pay for the wall. Mexican President Enrique Pena Nieto is due visit the White House next week to discuss border security issues and extensive trade between the two neighbors.
Trump has said building the wall will be easy, though others are not as confident of that, noting the rough terrain along the border, with regular peaks and valleys. Some of the property along the border is owned privately, and the owners say they oppose construction of a wall.
Also Wednesday, Trump targeted several hundred U.S. cities that by law or their political decisions have declared themselves "sanctuary cities," with their law enforcement agencies refusing to help federal agents identify undocumented immigrants so they could be detained and eventually deported.
Spicer said the president would attempt to block federal funding to the cities that showed "disregard for our laws." The cities individually could lose millions of dollars in assistance from the national government for a range of local programs. Many of the cities, including some of the biggest in the country, are in states that Trump won in the November election.
WATCH: Spicer on immigration officers, sanctuary cities
Even with Trump's immigration decrees, the new administration is grappling with how to deal with former President Barack Obama's order allowing immigrant children who entered the U.S. illegally when their parents crossed the border to stay in the U.S. for two years without fear of deportation. Many of the children know only the U.S. as their home and now are students or are working in the country.
Immigration hard-liners want these children deported, along with their parents, but their supporters call them "Dreamers" and have advocated allowing them to stay in the U.S.
Spicer said Trump officials would review the cases of the undocumented children "in a humane way."
On the campaign trail, Trump said everyone in the U.S. illegally would be subject to deportation, but subsequently he softened his stance and said only those with criminal records would be targeted initially, with the fate of law-abiding immigrants considered later.
Obama said his priority was to protect Americans, while also working to help immigrants who had been pushed from their homes by war, terrorism and political instability.
The Obama administration said refugees were "the most thoroughly screened travelers" to the United States and were required to undergo security checks, examination of biographic and biometric data, vetting by law enforcement and intelligence agencies, and extensive interviews before they were allowed into the country. For many refugees, the process takes up to two years to complete.
In 2016, the U.S. admitted about 85,000 refugees, including more than 12,500 Syrians. Obama set a goal for the 2017 fiscal year, which began in October, of 110,000 refugee admissions.