US President Donald Trump insists the US will still build a wall along its border with Mexico, despite ending the longest-ever US government shutdown without securing funds for the project.
On Twitter, Mr Trump said the deal to temporarily reopen government was "in no way a concession" on the wall.
The bipartisan agreement announced on Friday covers just three weeks.
Mr Trump indicated he might trigger another shutdown or declare a national emergency if his demands are not met.
The Republican president has vowed to reject any budget unless Congress includes $5.7bn (£4.3bn) to fund his signature campaign pledge.
The Democratic Party, which controls the House of Representatives, has flatly refused.
In a tweet on Saturday, Mr Trump said negotiations between Democrats and Republicans would start immediately but would not be easy because both sides were "very dug in".
In recent weeks Mr Trump has taken a hard line against thousands of migrants arriving at the US southern border.
"The case for national security has been greatly enhanced by what has been happening at the border and through dialogue. We will build the Wall!" he tweeted.
How did the shutdown end?
On Friday, the Senate and House unanimously passed a bill to temporarily end the shutdown, after which President Trump signed the bill into law.
Following the votes in Congress Mr Trump tweeted that his decision was not a concession but was "taking care of the millions of people who were getting badly hurt by the shutdown".
Most US media saw President Trump's move as yielding to political pressure after the unprecedented 35-day shutdown.
Speaking in the White House Rose Garden, Mr Trump said federal workers affected by the political standoff, whom he called "incredible patriots", would receive full back-pay.
Mr Trump also said he would not yet resort to "a very powerful alternative" - an apparent reference to declaring a national emergency.
Analysts say this could divert military funding towards building the border wall but would provoke constitutional uproar and legal challenges.
How bad was the shutdown?
On Friday, about 800,000 civil servants missed another payday amid the five-week closure of about a quarter of the federal government.
Earlier, hundreds of flights were grounded or delayed at US airports because of unpaid air traffic controllers calling in sick.
The Federal Aviation Administration (FAA) halted arrivals for about an hour at New York's LaGuardia Airport.
Flights were also delayed at Newark Liberty International Airport and Philadelphia International Airport because of staff shortages, the FAA said.
Meanwhile, thousands of Internal Revenue Service (IRS) employees failed to show up after they were ordered to return to work unpaid, the Washington Post reported.
The Trump administration recalled 26,000 IRS workers this week to handle the looming tax filing season.
But about 14,000 of them did not come back as of Tuesday, IRS officials told members of Congress.
In a video message to agents on Friday, FBI Director Christopher Wray said: "I'm about as angry as I've been in a long, long time."
Of the shutdown's effects on his agency, he said: "It's mind-boggling, it's short-sighted, and it's unfair."
His remarks came after an FBI report this week revealed its resources were at "breaking point".