WASHINGTON, United States (AFP) — President Donald Trump insisted Monday that the United States would not become a “migrant camp,” as he faced soaring pressure to end the separation of immigrant families on America’s southern border.

While top administration officials stood by Trump’s policy of “zero tolerance” towards unauthorised border crossers, and insisted children were being held in humane conditions, criticism swelled from rights groups and within the president’s own Republican Party.

With the US border crisis shaping up as a critical challenge of his presidency, Trump stood defiant even as Democratic lawmakers accused authorities of keeping children in “cages” separate from their incarcerated parents and Amnesty International likened the practice to “torture.”

“The United States will not be a migrant camp, and it will not be a refugee holding facility,” Trump said at the White House.

“You look at what’s happening in Europe, you look at what’s happening in other places, we can’t allow that to happen to the United States,” he said. “Not on my watch.”

Earlier Monday Trump barged into an immigration row rocking Europe, where countries have clashed on the issue, saying the continent made a “big mistake” by allowing in migrants.

The US leader has repeatedly stoked fears of migrant-driven crime to advance his anti-immigration agenda.

On the home front, Trump has said he wants family separations to end, but has refused to take responsibility — instead blaming Democrats, the minority party in Congress, whom he accuses of blocking legislation on the broader issue of illegal immigration.

“CHANGE THE LAWS!” Trump bellowed on Twitter.

Official data shows about 2,000 children have been separated from their parents or guardians since early May, when the administration said it would arrest and charge all migrants illegally crossing the Mexican border, regardless of whether they were seeking asylum. Since children cannot be sent to the facilities where their parents are held, they are separated from them.

The United Nations has slammed the practice as unconscionable, with Secretary-General Antonio Guterres offering rare criticism of the United States as his office said “children must not be traumatized by being separated from their parents.”

Rights group Amnesty International blasted the administration’s “spectacularly cruel” policy which has resulted in frightened children pried from their parent’s arms and taken to overflowing detention centers.

“This is nothing short of torture,” said Erika Guevara-Rosas, Amnesty’s Americas Director. Bracing for more child arrivals, US authorities plan to build camps at military bases in Texas. Amid deep divisions, congressional Republicans are drafting legislative options to address the crisis, with possible votes later this week.

“Some in the administration have decided that this cruel policy increases their legislative leverage. This is wrong,” said Republican Senator Ben Sasse, an occasional Trump critic. “Americans do not take children hostage, period.”

– ‘Utter atrocity’ –

Democrats, meanwhile, stepped up their opposition, with lawmakers conducting a second straight day of visits Monday to processing and detention facilities in Texas, including a converted Walmart supermarket housing some 1,500 immigrant children. Lawmakers spoke of children being held behind chain-link fencing inside the centers.

“I went into these facilities yesterday. They are cages,” House Democrat Mark Pocan said.

The Democratic fury was loud and unsparing.

“President Trump’s family separation policy leaves a dark stain on our nation,” House Minority Leader Nancy Pelosi said in a statement.

“Ripping vulnerable little children away from their parents is an utter atrocity that debases America’s values and our legacy as a beacon of hope, opportunity and freedom.”

First Lady Melania Trump made a rare foray into politics Sunday, saying she “hate” to see families separated, and calling for bipartisan immigration measures to fix the issue — but stopping short of denouncing her husband’s policy.

Democratic former president Bill Clinton denounced the policy as did Laura Bush, wife of Republican ex-president George W. Bush, in a poignant message retweeted by her successor as first lady, Michelle Obama.

Immigration is one of the most divisive issues roiling American politics.

Homeland Security Secretary Kirstjen Nielsen insisted that “we do not have a policy of separating families at the border. Period.”

But in practice, the number of separations has jumped since Attorney General Jeff Sessions announced that all migrants illegally crossing the US border with Mexico would be arrested. The American Academy of Pediatrics has warned that separating vulnerable immigrant families causes “irreparable harm.” One Honduran asylum seeker killed himself in detention after being separated from his wife and three-year-old son last month, The Washington Post reported. In a speech to the National Sheriff’s Association on Monday, Sessions repeated administration concerns that smugglers were posing as parents of children in order to gain US entry, saying it would be wrong to “ignore” border security laws.

“We do not want to separate children from their parents. We do not want adults to bring children into this country unlawfully either, placing them at risk,” he said.

“If we build the wall, if we pass legislation to end the lawlessness, we won’t face these terrible choices.”