A day after vowing to use the U.S. military to stop illegal immigration on the southern border, President Donald Trump on Wednesday approved plans to use National Guard forces to bolster immigration enforcement efforts, as top administration officials joined with the President in calling on Congress to change U.S. immigration laws.

"The President has directed the National Guard personnel be deployed to the southern border," said Homeland Security Secretary Kirstjen Nielsen in a briefing at the White House, as she said it was time for Congress to help by making major changes to federal immigration laws.

"It's time to act," Nielsen said.

The DHS Secretary said while the number of people coming across the border dropped to forty year lows after Mr. Trump took office, those numbers have snapped back.

"We have seen the numbers rise from forty year lows to their previous levels," Nielsen told reporters at the White House, again saying that Congress must make changes to end what's known as "catch and release."

Nielsen said the current situation provides what she labeled a "magnet of lawlessness, which is bringing more people into the U.S. illegally.

There was no final agreement as yet on how many National Guard forces would be sent to the border region, an effort which was undertaken in 2005 by President George W. Bush, and again in 2010 by President Barack Obama.

"It will be as many as is needed to fill the gaps today," Nielsen said, saying final numbers had not yet been determined.

The Bush Administration used nearly 6,000 members of the Guard, while the Obama Administration effort was smaller, at 1,200.

Like those previous efforts, National Guard troops are used in support roles, rather than in direct immigration enforcement, which is left to the Border Patrol and other federal agents.

Nielsen also said there were discussions ongoing about building wall at a spot where there is land already owned by the military that's along the border.

Asked why the Trump Administration was suddenly moving on this plan, Nielsen acknowledged that the President is 'frustrated' by the situation involving immigration, and frustrated by the lack of action in Congress on DACA and other immigration questions.

It wasn't clear when the first Guard forces would actually reach the border area to support immigration efforts, as Nielsen acknowledged that discussions were now underway with the Governors of Texas, Arizona, New Mexico and California.