Donald Trump has warned it could be "a long stay" as he negotiates with Democrats to end a partial US government shutdown.
The US president said border security remained at the centre of discussions after he demanded $5bn (£4bn) to fund the construction of a wall along the US border with Mexico.
The partial shutdown comes after Republicans in the Senate failed to secure the votes needed to approve the federal funds.
Mr Trump tweeted on Saturday: "I am in the White House, working hard. News reports concerning the Shutdown and Syria are mostly FAKE.
"We are negotiating with the Democrats on desperately needed Border Security (Gangs, Drugs, Human Trafficking & more) but it could be a long stay."
I am in the White House, working hard. News reports concerning the Shutdown and Syria are mostly FAKE. We are negotiating with the Democrats on desperately needed Border Security (Gangs, Drugs, Human Trafficking & more) but it could be a long stay. On Syria, we were originally…
— Donald J. Trump (@realDonaldTrump) December 22, 2018
Vice president Mike Pence and White House officials were on Capitol Hill late on Friday night trying to broker a compromise over funding for the wall, which is staunchly opposed by Democrats.
Without a deal, funding for around 25% of the government expired at midnight (5am GMT).
Nine cabinet-level departments and dozens of agencies – including homeland security, transportation, interior, agriculture, state and justice – are affected by the shutdown.
Mr Trump had said any impending shutdown could last "a very long time" as he blamed Democrats over the failure to agree a deal on spending.
Earlier this week, he said: "This is our only chance that we'll ever have, in my opinion, because of the world and the way it breaks out, to get great border security."
But on Friday, he said he hoped the shutdown would not last long.
In a video on his Twitter account he said: "We're going to have a shutdown. There's nothing we can do about that because we need the Democrats to give us their votes."
The disruption affects 800,000 federal employees. About 420,000 were deemed essential workers and will work unpaid in the lead-up to Christmas.
An additional 380,000 employees will stay at home without pay.
Democratic leaders Nancy Pelosi and Chuck Schumer said Mr Trump "threw a temper tantrum and convinced House Republicans to push our nation into a destructive Trump shutdown in the middle of the holiday season".
Looking for a way past the stalemate, Mr Trump said he would accept money for a "steel slat barrier" complete with spikes on top, which the leader said would be as effective as his promised wall while being "at the same time beautiful".
The wall was a key promise during Mr Trump's 2016 election campaign, which he insisted would be paid for by Mexico.
The impasse comes amid tension in Washington following Mr Trump's decision to withdraw US troops from Syria, which prompted the resignation of defence secretary Jim Mattis.
Brett McGurk, US special envoy for the global coalition to defeat Islamic State, quit his post on Saturday in opposition to the move.
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Addressing the issue on Twitter, Mr Trump said: "On Syria, we were originally going to be there for three months, and that was seven years ago – we never left.
"When I became President, ISIS was going wild. Now ISIS is largely defeated and other local countries, including Turkey, should be able to easily take care of whatever remains. We're coming home!"