Trump says US not 'migrant camp' amid family separation crisis

President Donald Trump vowed 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 unauthorized 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, 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, for blocking legislation on the broader issue of illegal immigration.

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"CHANGE THE LAWS!" Trump bellowed on Twitter.

New Department of Homeland Security data shows that 2,342 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.

In heartbreaking audio released by transparency group ProPublica, several Central American children separated from their parents are heard desperately sobbing and wailing, some so hard they almost cannot breathe.

"Mommy! I want to go with dad," a young girl is heard crying out.

The United Nations slammed the practice as unconscionable, while rights group Amnesty International blasted a "spectacularly cruel" policy which has resulted in frightened children pried from their parent's arms and taken to overflowing detention centres.

"This is nothing short of torture," said Amnesty's Americas director Erika Guevara-Rosas.

US public opinion appears divided along partisan lines on the family separations, with two-thirds of all American voters opposed, but 55 per cent of Republicans supporting the policy, according to a Quinnipiac University National Poll.

'Utter atrocity'

A Republican-led Congress is 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."

A disgusted Republican Senator John McCain tweeted: "The administration's current family separation policy is an affront to the decency of the American people, and contrary to principles and values upon which our nation was founded. The administration has the power to rescind this policy. It should do so now."

And Democrats stepped up their opposition, as lawmakers conducted a second straight day of visits to processing and detention facilities, including a converted Walmart supermarket in Texas housing some 1,500 immigrant children.

Lawmakers spoke of children being held behind chain-link fencing inside the centres.

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

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."

Pelosi was among 14 House Democrats who visited Casa San Diego, a southern California facility housing 62 children, many of whom had fled gang violence from Central American nations like Honduras.

"President Trump, do the decent thing, pick up the phone, stop this unconscionable policy," Congresswoman Judy Chu said.

Amid the outcry, independent investigative news organisation Pro Publica published audio obtained from inside a US Customs and Border Protection facility in which children are heard wailing.

"I don't want them to stop my father," a distraught girl's voice can be heard, as others cried in the background. "I don't want them to deport him."

'Not' controversial

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

Trump's own wife, First Lady Melania Trump, said she hates to see families separated -- although she stopped short of criticising her husband's policies.

Democratic former president Bill Clinton and Trump's 2016 rival Hillary Clinton each denounced the practice, 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.

Homeland Security Secretary Kirstjen Nielsen insisted that "we do not have a policy of separating families at the border," but warned that anyone crossing the border illegally would face prosecution, with the result of their children being taken away.

"What has changed is that we no longer exempt entire classes of people who break the law," she said. "This is not a controversial idea."