Congress members trickled back into Washington Thursday but there was little hope of ending the government shutdown sparked by a row with President Donald Trump over his demand for US-Mexico border wall construction.
The Senate was in session after the Christmas break, but very few lawmakers were likely to appear and formal negotiations over the budget impasse were not expected.
A lapse in funding to parts of the government meanwhile entered a sixth day.
Trump, apparently not sleeping after a gruelling roundtrip to Iraq -- his first visit to US combat troops since being elected -- indicated on Twitter that he was in no mood to compromise.
He wants USD 5 billion for extensions and improvements to a Mexico border barrier that he has made the centerpiece of his domestic political platform, arguing that the United States needs protection from illegal immigration.
Opponents, who include some of Trump's own Republicans, accuse the president overhyping the immigration problem for political gain and say that a wall is not the best form of border security.
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In retaliation Trump is refusing to sign a wider spending package, forcing large parts of the government to hibernate as 800,000 federal employees temporarily go unpaid.
Neither side has budged in the game of political chicken and on Thursday Trump remained defiant.
"Have the Democrats finally realised that we desperately need Border Security and a Wall on the Southern Border," he tweeted, barely three hours after arriving from the Iraq trip.
"Need to stop Drugs, Human Trafficking,Gang Members & Criminals from coming into our Country," he said.
Partial government shutdowns are not an unusual weapon in Washington budget negotiations, where party divides make cooperation a rarity.
But the rancor has spiralled under Trump's abrasive administration and is set to go even higher in January when the Democrats take over the House of Representatives, following their midterm election victory.
The mess has contributed to worries over the outlook for the US economy in 2019, following a surging 2018 performance.
The stock market had plummeted in recent days before making a record recovery on Wednesday, as investors reeled from Trump's barrage of criticism against the independent Federal Reserve.
Continuing the see-saw performance, Wall Street opened sharply lower Thursday.
Large sections of the nearly 2,000-mile border with Mexico are already divided by fences and other barriers.
But immigrants -- some fleeing danger and others just looking for jobs -- continue to cross illegally.
Trump's critics say that he is trampling over legally protected asylum rights and argue that resources should be channelled into higher-tech alternatives to a wall.
Managing the flow of illegal border crossers has been complicated by a shift from single men to more vulnerable families, including small children.
Two children from Guatemala have died while in custody of US authorities this month and Homeland Security Secretary Kirstjen Nielsen said that "extraordinary protective measures" were required to handle the flow.
US Customs and Border Protection Commissioner Kevin McAleenan warned Wednesday that the agency was unable to cope with the thousands of arrivals, as most facilities were built decades ago for men arriving alone.
"We need help from Congress. We need to budget for medical care and mental health care for children in our facilities," he told CBS News.