President Donald Trump said Wednesday that the U.S. would be "taking strong action today" on border security.

"The Democrats stand in our way – they want people to pour into our country unchecked....CRIME! We will be taking strong action today," Trump tweeted minutes before 7:30 a.m. ET.

It wasn't immediately clear what sort of action the president was referring to. CNBC reached out to a White House representative for clarification and did not get an immediate response.

Later Wednesday, however, Homeland Security Secretary Kirstjen Nielsen announced that her department, along with the Pentagon and border states' governors, would work together to deploy National Guard forces at the border.

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Trump has ramped up his rhetoric in recent weeks as he pushes for more stringent border security and immigration laws. On Tuesday, Trump said he wanted to send U.S. military forces to the southern border with Mexico while he awaits construction on a border wall — which was a key pledge in campaign for president.

Trump has discussed the possibility of the Defense Department using funds to pay for the wall, although lawmakers have pushed back against that suggestion. The Pentagon, meanwhile, has said that it is already backing up the Department of Homeland Security on protecting the border, although Defense's role could expand.

"There are a number of ways the Department of Defense is already supporting the DHS border security mission," Pentagon spokeswoman Dana White said late Tuesday. "We are still in consultation with the White House about ways we can expand that support."

Nielsen, the Homeland Security secretary, said Wednesday that the White House has put together legislation to address border security.

"The administration has drafted legislation and we will be asking Congress again for the legal authority and resources to address this crisis," she said. "Based on conversations with congressional leadership, I am optimistic."

The president was irritated by a massive omnibus spending bill he signed late last month to keep the government funded. He had been pushing for about $25 billion to fund the wall, but the bill included $1.6 billion for border security — including restrictions on how the funds could be used.

Trump has characterized the amount as a down payment on the barrier. During the campaign he had repeatedly said Mexico would pay for the wall.

CNBC's Amanda Macias and Jacob Pramuk contributed to this report.