WASHINGTON — President Donald Trump moved aggressively to tighten the nation’s immigration controls Wednesday, signing executive actions to jumpstart construction of a U.S.-Mexico border wall and block federal grants from immigrant-protecting “sanctuary cities.”

“Beginning today the United States of America gets back control of its borders,” Trump declared during a visit to the Department of Homeland Security. “We are going to save lives on both sides of the border.”

Trump cast his actions as fulfillment of a campaign pledge to enact hard-line immigration measures, including construction of a wall paid for by Mexico. With the families of Americans killed by people living in the U.S. illegally sitting in the audience, Trump said, “When it comes to public safety, there is no place for politics.”

Sen. David Perdue, R-Georgia, applauded Trump’s measures, saying current immigration laws must be enforced.

“Job one is to make it easier to remove felons who are here illegally and pose a risk to the safety of Americans. Simultaneously, our federal government should finally crack down on the hundreds of sanctuary cities refusing to enforce our laws by choosing to harbor criminals and illegal immigrants,” Perdue said in a news release. “President Trump’s actions are a good first step toward fixing our immigration system and solving our national security crisis.”

Sen. Johnny Isakson, R-Georgia, offered similar praise.

“I have always drawn a clear distinction between legal and illegal immigration, and the defense of our nation begins with securing our borders and ending the opportunity for illegal entry,” Isakson said in a news release. “Those who come to our country legally should be welcomed to share in the pursuit of the American dream.”

U.S. Rep. Doug Collins, R-Gainesville, gave his support on Twitter: “#Immigrationreform orders from #POTUS today will protect our citizens and our borders & ensure everyone follows the law. #KeepingPromises.”

Funding for the border wall project is murky. While Trump has repeatedly promised that Mexico will pay for it, U.S. taxpayers are expected to cover the initial costs and the new administration has said nothing about how it will compel Mexico to reimburse the money. One of the executive actions Trump signed Wednesday appears to signal that he could restrict aid to Mexico.

In an interview with ABC News earlier Wednesday, Trump said, “There will be a payment; it will be in a form, perhaps a complicated form.”

Mexican President Enrique Pena Nieto, who has insisted his country will not pay for a wall, is expected to meet with Trump at the White House next week, despite calls from some lawmakers for him to cancel his visit.

Congressional aides say there is about $100 million of unspent appropriations in the Department of Homeland Security account for border security, fencing and infrastructure. That would allow planning efforts to get started, but far more money would have to be appropriated for when construction got underway.

Trump has insisted many times the border structure will be a wall. The order he signed referred to “a contiguous, physical wall or other similarly secure, contiguous and impassable physical barrier.”

The president’s orders also call for hiring 5,000 additional border patrol agents, though the increase is subject to congressional approval. He also moved to end what Republicans have labeled a catch-and-release system at the border. Currently, some immigrants caught crossing the border illegally are released and given notices to report back to immigration officials at a later date.

Later in the week, Trump is expected to sign orders restricting the flow of refugees into the United States. His current proposal includes at least a four-month halt on all refugee admissions, as well as a temporary ban on people coming from some Muslim-majority countries, according to a source from a public policy organization that monitors refugee issues. The person was briefed on the details of that proposed action by a government official and outlined the plan to The Associated Press.

The public policy organization source insisted on anonymity in order to outline the plans ahead of the president’s official announcements.

Trump campaigned on pledges to tighten U.S. immigration policies, including strengthening border security and stemming the flow of refugees. His call for a border wall was among his most popular proposals with supporters, who often broke out in chants of “build that wall” during rallies.

In response to terrorism concerns, Trump controversially called for halting entry to the U.S. from Muslim countries. He later turned to a focus on “extreme vetting” for those coming from countries with terrorism ties.

To build the wall, the president is relying on a 2006 law that authorized several hundred miles of fencing along the 2,000-mile frontier. That bill led to the construction of about 700 miles of various kinds of fencing designed to block both vehicles and pedestrians.

The Secure Fence Act was signed by then-President George W. Bush, and the majority of that fencing in Texas, New Mexico, Arizona and California was built before he left office. The last remnants were completed after President Barack Obama took office in 2009.

The Trump administration also must adhere to a decades-old border treaty with Mexico that limits where and how structures can be buil. The 1970 treaty requires that structures cannot disrupt the flow of the rivers, which define the U.S.-Mexico border along Texas and 24 miles in Arizona, according to The International Boundary and Water Commission, a joint U.S.-Mexican agency that administers the treaty.

Trump’s order to crack down on sanctuary cities — locales that don’t cooperate with immigration authorities — could cost individual jurisdictions millions of dollars.  But the administration may face legal challenges, given that some federal courts have found that local jurisdictions cannot hold immigrants beyond their jail term or deny them bond based only a request from immigration authorities.

It appeared as though the refugee restrictions were still being finalized. The person briefed on the proposals said they included a ban on entry to the U.S. for at least 30 days from countries including Iran, Iraq, Libya, Somalia, Sudan and Yemen, though the person cautioned the details could still change.

There is also likely to be an exception for those fleeing religious persecution if their religion is a minority in their country. That exception could cover Christians fleeing Muslim-majority nations.

As president, Trump can use an executive order to halt refugee processing. Bush used that same power in the immediate aftermath of the Sept. 11 attacks. Refugee security vetting was reviewed and the process was restarted several months later.