0900 GMT February 25, 2018
Although leaders of President Donald Trump's Republican Party and the opposition Democrats said progress had been made in a weekend of talks, they pushed back a vote scheduled for 1:00 a.m. (0600 GMT) Monday for another 11 hours.
After special weekend sessions of Congress which had seen bitter recriminations traded by both parties, Senate Majority Leader Mitch McConnell pledged to address Democrat concerns over key issues such as immigration reform in a speech to the chamber late Sunday.
The Senate's top Democrat Chuck Schumer responded by saying he was "happy to continue my discussion with the majority leader about reopening the government" but added that the parties were "yet to reach an agreement on a path forward."
McConnell then called for Congress to reconvene for another vote on a stopgap funding measure at noon, a proposal which was nodded through.
Hopes that the shutdown, which began at midnight Friday, could be limited to the weekend had been raised Sunday when a bipartisan group huddled for hours on trying to end the standoff, but they ultimately failed to resolve all their differences.
At the heart of the dispute is the issue of undocumented immigration.
Democrats have accused Republicans of poisoning chances of a deal and pandering to Trump's populist base by refusing to back a program that protects an estimated 700,000 "Dreamers" – undocumented immigrants who arrived as children – from deportation.
Democrats have refused to go along with the temporary federal funding request unless it addresses the Deferred Action for Childhood Arrivals program in part because they fear Republican leaders will not act to protect DACA recipients before deportations would begin in large numbers in March.
But in a signal to Democrats, McConnell committed on the Senate floor to addressing immigration in timely fashion.
"Should these issues not be resolved by the time the funding bill before us expires on February 8th, 2018, assuming that the government remains open, it would be my intention to proceed to legislation that would address DACA, border security and related issues," McConnell said.
But that commitment means little on the other side of the Capitol, where House Republicans told reporters they would not be bound by any agreement reached in the Senate to address immigration.
Essential federal services and military activity are continuing, but even active-duty troops will not be paid until a deal is reached to reopen the US government.
There have been four government shutdowns since 1990. In the last one, more than 800,000 government workers were put on temporary leave.
"We're just in a holding pattern. We just have to wait and see. It's scary," Noelle Joll, 50, a furloughed US government employee, told AFP in Washington.