US President Donald Trump has made his first TV address to the nation from the Oval Office, escalating a stand-off with Congress that has led to an 18-day partial government shutdown.
Mr Trump insisted on funding for his long-promised US-Mexico border wall.
However, he did not declare an emergency that would enable him to bypass the lower house of Congress now controlled by the opposition Democrats.
Democratic leaders accused him of holding the American people hostage.
The Republican president wants $5.7bn (£4.5bn) to build a steel barrier, which would deliver on his signature campaign pledge.
But Democrats – who recently took control of the House of Representatives – are adamantly opposed to giving him the funds.
The ongoing closure of a quarter of federal agencies is the second-longest in history, leaving hundreds of thousands of government workers unpaid.
In an eight-minute address on Tuesday night carried live by all the major US television networks, Mr Trump said the federal government remained shut because of the Democrats.
He said of the situation at the border: “This is a humanitarian crisis, a crisis of the heart and a crisis of the soul.”
Mr Trump said an as-yet-unratified revamp of the North American Free Trade Agreement would pay for the wall, a claim previously disputed by economists.
The president also said that 90% of heroin sold in the US came from Mexico, though US government figures make clear all but a small percentage is smuggled through legal points of entry.
Mr Trump correctly pointed out that Democrats have in the past supported a physical barrier.
In 2006, senators Chuck Schumer, Barack Obama, Hillary Clinton and Joe Biden voted in favour of 700 miles (1,120km) of fencing on the nearly 2,000-mile border under the Secure Fence Act.
Mr Trump cited cases of American citizens “savagely murdered in cold blood” by undocumented immigrants.
“How much more American blood will be shed before Congress does its job?” he asked.
On Wednesday, he will seek to stiffen the resolve of fellow Republicans on Capitol Hill before hosting congressional leaders for talks at the White House.
Mr Trump heads to the south-western border on Thursday.
In a brief rebuttal, House Speaker Nancy Pelosi and Senate minority leader Chuck Schumer demanded that Mr Trump end the shutdown.
Mrs Pelosi said: “The fact is the women and children at the border are not a security threat, they are a humanitarian challenge.”
The California congresswoman added: “And the fact is President Trump must stop holding the American people hostage, must stop manufacturing a crisis, and must reopen the government.”
Mr Schumer accused Mr Trump of trying to “govern by temper tantrum”.
“President Trump has appealed to fear, not facts. Division, not unity,” the New York senator said.
He concluded: “The symbol of America should be the Statue of Liberty, not a 30-foot wall.”
Democrats argue that maintenance of existing border fencing, hi-tech tools to scan vehicles crossing at ports of entry, and hiring more personnel would be cheaper and more effective than a wall.
Analysis by Anthony Zurcher, BBC News
There were two audiences for Donald Trump’s address to the nation on Tuesday night. The first was the American public, which polls indicate are generally uninterested in his border wall proposal and view the president as responsible for the government shutdown. The other was Republicans in Congress, who Mr Trump needs to keep in the fold if he is going to get anything out of this extended political confrontation.
It seems unlikely that the president said anything that will move the needle with the public at large. The arguments were familiar – and some have already been debunked. The president has been saying there’s a “crisis” at the border practically since he first started campaigning for president.
As for congressional Republicans, the speech was a demonstration that Mr Trump is going to use every arrow in his presidential quiver to get his wall.
The president may have bought himself a bit more time for negotiations. It’s just not clear what good it will do him.
Though both Democrats and Republicans agree more border security is needed, critics have accused Mr Trump of greatly exaggerating the problem.
The number of illegal border crossings is down from 1.6 million in 2000 to fewer than 400,000 last year.
And research indicates that undocumented immigrants are much less likely to commit crime than native-born American citizens.
The White House suggested at the weekend that thousands of terrorists were caught attempting to cross the US-Mexico border, but in fact all but a handful were stopped at airports.
Mr Trump is backed by most of his party, though on Tuesday moderate Republican Senator Lisa Murkowski of Alaska joined Democrats in calling for an end to the shutdown before the border wall issue is resolved.
Her fellow Republican senators, Susan Collins of Maine and Cory Gardner of Colorado, issued similar appeals last week.
A new opinion poll suggests just over half of Americans (51%) blame President Trump for the government shutdown.
However, 77% of Republicans said they supported his refusal to approve a budget without taxpayer dollars for the US-Mexico border wall, according to the Reuters/Ipsos poll.
Though Mr Trump did not declare a national emergency on Tuesday night, analysts say he may still do so before the impasse comes to an end.
Such a dramatic escalation of the standoff might allow him to access military spending to fund his barrier, which remains un-built two years into his presidency.
But the president would be accused of usurping Congress’s constitutional power of the purse, and the move would be bogged down in a quagmire of legal challenges.
Some correspondents have speculated that he may ultimately resort to such a declaration as a last-ditch tactic to allow him to reopen the government without losing face to Democrats.