President Donald Trump has threatened to close the US border with Mexico if Democrats in Congress do not agree to fund the construction of a border wall.
Mr Trump tweeted on Friday morning that "we will be forced to close the Southern Border entirely" unless a funding deal is reached with "the Obstructionist Democrats".
Mr Trump's demand for money to build the border wall and Democrats' refusal to give him what he wants has caused a partial government shutdown that is nearly a week old.
Congress adjourned for the week without a resolution in sight.
The shutdown has led to hundreds of thousands of federal workers being off work and citizens who count on some public services beginning to feel the pinch.
White House press secretary Sarah Sanders said of Democrats: "They've left the table altogether, so of course we are far apart."
'We expect this to go on for a while'
Incoming acting chief of staff Mick Mulvaney complained that Democrats were ignoring an offer from the White House to agree to lower funding levels to build the wall. Mr Mulvaney said the offer was made on Saturday but Democrats are no longer considering that option.
He said: "There's not a single Democrat talking to the President of the United States about this deal."
He added of the shutdown: "We do expect this to go on for a while."
After a weekend and two holiday days for federal employees, Wednesday was the first regularly scheduled workday affected by the closure of a variety of federal services.
The shutdown started on Saturday when funding lapsed for nine Cabinet-level departments and dozens of agencies.
Roughly 420,000 workers were deemed essential and are working unpaid, while an additional 380,000 have been put on hold.
The impasse over government funding began last week, when the Senate approved a bipartisan deal keeping government open into February.
That bill provided $1.3 billion (£1 billion) for border security projects but not money for the wall. At Mr Trump's urging, the House of Representatives approved that package and inserted the $5.7 billion (£4.5 billion) he had requested.
But Senate Republicans lacked the votes they needed to force the measure through their chamber. That jump-started negotiations between Congress and the White House but the deadline came and went without a deal.