WASHINGTON — President Donald Trump said Monday he plans to give a prime-time speech on border security and visit the U.S.-Mexico border this week amid a partial federal government shutdown over his insistence on building a wall there.

Trump tweeted that he would "Address the Nation on the Humanitarian and National Security crisis on our Southern Border" Tuesday night at 9:00 p.m. ET shortly after the White House announced he would visit the border this Thursday.

It was not clear how many news networks intended to carry the speech live.

"President @realDonaldTrump will travel to the Southern border on Thursday to meet with those on the frontlines of the national security and humanitarian crisis," White House press secretary Sarah Sanders wrote on Twitter Monday. "More details will be announced soon."

The announcements come after a weekend in which White House negotiators, led by Vice President Mike Pence, and congressional staff made little apparent headway in trying to resolve the impasse, which has led several federal agencies — accounting for about a quarter of the federal government — to cease all functions but those deemed most "essential" to the public.

Trump has asked Congress for nearly $6 billion in funding for a border wall, while House Speaker Nancy Pelosi, D-Calif., has said that she will not agree to give him a dime for that purpose.

Before the partial shutdown on Dec. 21, the Senate unanimously passed a government-funding bill providing more than $1 billion for border security but none of that money was earmarked for a wall. The House, then controlled by Republicans, passed a version that included Trump's request.

Those two bills died as the new Congress began Jan. 3, and the House, now led by Democrats, has since passed bills to re-open the government that do not include wall money. Senate Majority Leader Mitch McConnell, R-Ky., has refused to take up that legislation because Trump has indicated that he won't sign it.

White House officials have been looking at ways to use existing legal authority and money already appropriated by Congress to build the wall if lawmakers do not provide the cash Trump wants.

"I may declare a national emergency dependent on what's going to happen over the next few days," the president said Sunday.

It's not clear exactly how Trump could use his power to declare a "national emergency" for the construction of a wall or where the money would come from. Under current law, the Defense secretary can transfer up to $4 billion between programs if he deems such a move to be in the "national interest." But he must notify Congress — which, in the past, has meant sign-off from top lawmakers who oversee defense spending — and it can't be for a purpose for which Congress has previously denied funding.