The US government shutdown is set to sow more disruption and political peril today after the Senate inched closer but ultimately fell short of an agreement that would have reopened federal agencies before the beginning of the workweek.

Senate Majority Leader Mitch McConnell and Democratic leader Chuck Schumer said negotiations last night lasted late into the evening, with a vote to break a Democratic filibuster on a short-term funding bill scheduled for noon today.

Under the proposal taking shape, Democrats would agree to a three-week spending measure – until February 8 – in return for a commitment from the Republican leadership in the Senate to address immigration policy and other pressing legislative matters in the coming weeks.

Despite the growing crisis, President Donald Trump has not appeared in public since Friday afternoon. Nor has he spoken to reporters or to identify his desired immigration policy – a policy which first sparked a standoff with the Democrats.

Rather, Mr Trump has been a relatively subdued player in the weekend debate. The White House said he was in regular contact with Republican leaders, but he has not reached out to any Democrats, a White House official said.

President Donald Trump speaks to the March for Life participants from the Rose Garden of the White House in Washington on January 19. (AAP)

The president today accused Democrats of prioritising services and security for noncitizens over US citizens.

"Not good," his first tweet said. In a second tweet, he said, "Democrats have shut down our government in the interests of their far left base. They don't want to do it but are powerless!"

Mr Trump's first tweet appeared to undercut comments by his legislative affairs director, Marc Short, who told CNN that the immigrants in question are law-abiding and "productive to our society". Mr Short says the administration wants to "find a pathway for them" to stay in the US.

Meanwhile Democrats appeared to be holding out for a firmer commitment from Mr McConnell.

"We have yet to reach an agreement on a path forward," Mr Schumer said late yesterday.

Mr McConnell's comments followed hours of behind-the-scenes talks between the leaders and rank-and-file lawmakers over how to end the display of legislative dysfunction, which began at midnight Friday after Democrats blocked a temporary spending measure.

Democrats have sought to use the spending bill to win concessions, including protections for roughly 700,000 younger immigrants brought illegally to the US as children.

Republicans have appeared increasingly confident that Democrats were bearing the brunt of criticism for the shutdown and that they would ultimately buckle.

The White House and GOP leaders said they would not negotiate with Democrats on immigration until the government is reopened.

There were indications yesterday that Democratic resolve was beginning to waver, with growing worries that a prolonged shutdown could prove to be an electoral headache for the party just as it has grown more confident about prospects in November midterm elections.

Senate Minority Leader Chuck Schumer, D-N.Y., explains to reporters how his negotiations with President Donald Trump broke down last week. (AAP)

Although they initially dug in on a demand for an immigration deal, Democrats had shifted to blaming the shutdown on the incompetence of Republicans and Mr Trump, seeming sensitive to being seen by voters as willing to tie up government operations to protect immigrants.

Democrats are facing intense pressure from their base to solve the issue over the young immigrants, commonly referred to as "Dreamers", and they are sceptical of Republicans' credibility when offering to take up the issue. Whether Mr Trump would back the emerging plan or any later proposal on immigration is an open question.

While lawmakers feuded, signs of the shutdown were evident at national parks and in some federal agencies. Social Security and most other safety-net programs were unaffected by the lapse in federal spending authority. Critical government functions continued, with uniformed service members, health inspectors and law enforcement officers set to work without pay.

Lawmakers were mindful that the political stakes would soar this morning, when thousands of federal workers would be told to stay home or, in many cases, work without pay.

What was still a weekend burst of Washington dysfunction could spiral into a broader crisis with political consequences in November.