The US homeland security secretary says the Trump administration will not apologise for separating undocumented immigrant children from their parents.
Kirstjen Nielsen told a police conference in Louisiana the young people are being well taken care of in US detention centres.
Photos went viral over the weekend showing children being held in fenced enclosures at a Texas facility.
The UN human rights chief has condemned the policy as "unconscionable".
"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.
"Illegal actions have and must have consequences. No more free passes, no more get out of jail free cards."
She continued: "It is important to note that these minors are very well taken care of – don't believe the press – they are very well taken care of.
"If you cross the border illegally," she added, "if you make a false immigration claim, we will prosecute you. If you smuggle aliens… we will prosecute you."
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."
Over the weekend, protesters rallied against the Trump administration's "zero tolerance" immigration crackdown, accusing White House and US immigration officials of cruelty.
US First Lady Melania Trump and former First Lady Laura Bush each weighed in on the new policy over the weekend.
Mrs Trump said through a spokeswoman that she "hates to see children separated from families".
Mrs Bush – who is married to George W Bush – wrote in a Washington Post op-ed that the policy was "cruel" and "immoral".
She said pictures from the detention centres were "eerily reminiscent" of Japanese-American internment camps during the Second World War.
US Attorney General Jeff Sessions also addressed the New Orleans sheriffs' conference on Monday, saying undocumented immigrants were exploiting the US system.
He said previous White House administrations had granted effective immunity from prosecution to those who illegally crossed the border with children, creating a "loophole".
"Why wouldn't you bring children with you if you know you will be released and not prosecuted?" he asked rhetorically.
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