President Trump has signed a proclamation directing the National Guard to be deployed to the U.S.-Mexico border, the White House announced Wednesday night. Mr. Trump said in a Wednesday memorandum to his secretaries of defense and homeland security and to his attorney general that the "situation at the border has now reached a point of crisis."

The document orders the secretary of defense to support the Department of Homeland Security in securing the southern border to stop the flow of drugs and people.

And it orders the agency heads to submit a report within 30 days outlining what other steps can be taken.

Get Breaking News Delivered to Your Inbox

Mr. Trump says "lawlessness" at the southern border is "fundamentally incompatible with the safety, security, and sovereignty of the American people," adding that his administration "has no choice but to act."

Mr. Trump has been frustrated by slow action on building his "big, beautiful wall" along the Mexican border -- the signature promise of his campaign -- as well as a recent uptick in illegal border crossings, which had plunged during the early months of his presidency. He has also been upset because the spending bill he grudgingly signed last month includes far less money for the wall than he'd hoped for.

Astrid Dominguez, director of the ACLU Border Rights Center, said in a statement that the president "is trying to create a crisis where there is none. This is another impulsive reaction to not getting his wall fully funded and a maneuver to distract the American public from the crisis he created for 800,000 young immigrants when he ended DACA, whose lives and futures are at risk.

"Military troops don't belong at the border; there is no security crisis and this deployment wastes valuable time and resources. Armed forces would further harm some of the safest communities in the U.S. at a time of record-low migration.

"This is an opportunity for governors and Congress to focus on the real issues and reject Trump's gimmicks."

The president's decision to send troops to the border caught his own administration by surprise, reports CBS News chief White House correspondent Major Garrett.

Federal law prohibits the use of active-duty service members for law enforcement inside the U.S., unless specifically authorized by Congress. But over the last 12 years, presidents have twice sent National Guard troops to the border to bolster security and assist with surveillance and other support.

Homeland Security Secretary Kirstjen Nielsen couldn't describe the size of the force, the estimated cost or the duration.

"I don't want to get ahead of the governors," she said at the White House Wednesday. "This is a partnership with them. As soon as the numbers are available we'll provide that."

President Obama sent 1,200 National Guard troops to the border in 2010, and President George W. Bush sent 6,000 in 2006.

When asked if this deployment will be more robust than the one during Mr. Bush's era. she replied, "It will be strong. It will be as many as is needed to fill the gaps that we have today is what I can tell you."