US President Donald Trump has said he has "no problem doing a shutdown" to pry funding from Congress for his planned border wall.
Hosting Italy's prime minister, he also told reporters he would "leave room for negotiation" on border security.
Congress must agree on spending to fund the government by 30 September, but a shutdown would be politically risky as mid-term elections loom in November.
The Republican president has repeatedly threatened a shutdown.
What did President Trump say?
"If we don't get border security after many, many years of talk within the United States, I would have no problem doing a shutdown," Mr Trump said at a joint press conference on Monday with Giuseppe Conte.
"We're the laughingstock of the world."
Mr Trump said the populist Italian premier grasped the issue of illegal immigration.
"We agreed that border security is national security - they are one and the same," the US president said after their Oval Office meeting.
"Like the United States, Italy is under enormous strain as the result of illegal immigration, and they fought it hard. Italy got tired of it, they didn't want it any longer."
Mr Trump said of Mr Conte: "I know he's taken a very firm stance on the border, a stance that few countries have taken, and frankly you're doing the right thing, in my opinion.
"And a lot of other countries in Europe should be doing it also."
At the same news conference, the US president offered to meet Iran's leaders anytime without preconditions.
Has President Trump made this threat before?
Yes. On Sunday, he fired off a flare on Twitter about a possible government shutdown.
I would be willing to “shut down” government if the Democrats do not give us the votes for Border Security, which includes the Wall! Must get rid of Lottery, Catch & Release etc. and finally go to system of Immigration based on MERIT! We need great people coming into our Country!— Donald J. Trump (@realDonaldTrump) July 29, 2018
He wants lawmakers to approve $25bn (£19bn) to fund the construction of a "big, beautiful wall" on the US-Mexico border, a signature promise of his election campaign.
Deadlocks over spending and immigration caused a three-day government shutdown in January this year and again a month later, though that one lasted just a few hours.
In March, Congress passed a bill with $1.6bn in border security funding, but most of it was to repair sections of an existing barrier along the US-Mexico border.
Mr Trump briefly threatened to veto that spending bill before ultimately signing it, though he said he would never approve such a budget again.
Some of his supporters were disappointed, believing he had passed up on his best opportunity to wring full wall funding from Congress.
Doesn't the president's party control Congress?
Republicans do indeed hold sway in both chambers on Capitol Hill.
But in June moderate members of the party in the US House of Representatives helped sink an immigration bill that was proposed by their conservative colleagues and backed by Mr Trump.
A shutdown would go into effect on 1 October, a month before the midterm elections, and pollsters are currently predicting Democrats could take control of the House.
Republicans distanced themselves from Mr Trump's threat on Monday.
"I'm not sure where the president is coming from," said South Dakota Senator John Thune, reports the New York Times.
Republican Senate leader Mitch McConnell said in a radio interview on Friday he did not think there would be another fiscal showdown.
"No, that's not going to happen," the Kentucky senator told WHAS radio station in Louisville on Friday.