President Donald Trump has said he will not allow the US to become a “migrant camp”, as he stood by his administration’s immigration crackdown.
“The United States will not be a migrant camp,” he said at the White House. “And it will not be a refugee-holding facility – it won’t be.”
Photos over the weekend showed undocumented children being held in fenced enclosures at a Texas facility.
The UN human rights chief has condemned the policy as “unconscionable”.
Mr Trump said on Monday: “You look at what’s happening in Europe, you look at what’s happening in other places.
“We cannot allow that to happen to the United States. Not on my watch.”
Earlier, he said European countries had made a big mistake by allowing in millions of migrants.
Mr Trump criticised Chancellor Angela Merkel of Germany in particular, saying her people were turning against their leaders because of the issue.
Mrs Merkel is in a migration dispute with her interior minister, Horst Seehofer, who wants to refuse migrants if they have already registered for asylum elsewhere in the EU.
The Republican president blamed Democrats for not coming to the table to negotiate immigration legislation.
Nearly 2,000 children have been separated from their parents at the border between mid-April and the end of May.
The administration’s “zero tolerance” policy entails criminally charging those entering the US illegally, including asylum seekers.
This has led to parents being separated from their children, who are not charged with a crime.
As a result, hundreds of children are being housed in detention centres, including warehouses and converted supermarkets.
Some shelters and foster homes have said they are running out of space.
On Sunday, Father’s Day, Democratic lawmakers visited shelters and processing facilities in New Jersey and Texas, demanding to see detainees.
Officials have also announced plans to erect tent cities that will hold hundreds more children in the Texas desert where temperatures regularly reach 40C (105F).
Democrats and some in Mr Trump’s own Republican Party have strongly condemned the administration.
The crackdown has even provoked fierce criticism from the president’s wife, Melania Trump, who said over the weekend she “hates to see children separated from families”.
Former First Lady Laura Bush meanwhile wrote in a Washington Post op-ed that the tactics were “immoral” and evoked Japanese-American internment camps during the Second World War.
Former Democratic presidential nominee Hillary Clinton said Mr Trump’s widely debunked claims that the family separations were mandated by law was “an outright lie”.
Massachusetts Governor Charlie Baker, a Republican, cited the “inhumane” policy on Monday as he reversed his decision to contribute National Guard resources to the southern US border to help enforce border security.
Most congressional Republicans, however, have declined to criticise Mr Trump over the policy.
A conservative commentator, Ann Coulter, claimed young people pictured crying at the border after being separated from parents were “child actors”.
“Do not fall for it, Mr President,” Ms Coulter said on Fox News.
US Homeland Security Secretary Kirstjen Nielsen said on Monday the undocumented children were being “very well taken care of” in US custody.
“Don’t believe the press,” she added.
“We will not apologise for the job we do or for the job law enforcement does for doing the job that the American people expect us to do,” she told the National Sheriffs’ Association annual conference in New Orleans, Louisiana.
“Illegal actions have and must have consequences. No more free passes, no more get out of jail free cards.”
Ms Nielsen was widely criticised on Sunday when she tweeted that her department does “not have a policy of separating families at the border. Period.”
Addressing the same conference, US Attorney General Jeff Sessions blamed previous White House administrations for allowing adults to illegally cross the border with children.
“Why wouldn’t you bring children with you if you know you will be released and not prosecuted?” he asked rhetorically.
Analysis by Tara McKelvey, White House reporter, BBC News
Kirstjen Nielsen has taken on a huge responsibility. Not only is she supposed to fix immigration, she’s dealing with a volatile boss.
He’s reportedly yelled at her, and I was in the room with them recently when strain in the relationship showed. During a briefing on hurricane preparedness, President Trump started to praise her work – only to blurt out: “What do I say about you?” She laughed, but it was an awkward exchange.
Also recently Chief of Staff John Kelly spoke to me and a few other reporters about Ms Nielsen, his protege, making it clear he’s tried to convince her to stay – though she’s been desperate to leave.
Like other officials, she’s reflecting the boss’ strategy: in the midst of blistering attacks, they’re digging in their heels, lashing out at the media and – this morning at least – showing they won’t be swayed.
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