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US First Lady Melania Trump has expressed concern over a controversial policy that separates families who illegally enter the country.
Mrs Trump "hates to see children separated from their families" and wants to see "successful immigration reform", her spokeswoman said.
Her comments follow growing controversy over President Donald Trump's "zero-tolerance" immigration policy.
Former First Lady Laura Bush also spoke out, labelling the policy "immoral".
In a recent six-week period there were nearly 2,000 family separations following a crackdown on illegal border crossings.
Adults who try to cross the border, many planning to seek asylum, are placed in custody and face criminal prosecution for illegal entry.
■ Why the US is separating migrant children from their parents
■ What is the policy in other countries?
■ US attorney general quotes Bible to defend separating families
■ Ivanka's mother and child photo sparks backlash
As a result, hundreds of minors are now being housed in detention centres, and kept away from their parents - a policy which rights groups have criticised as unprecedented.
What's been said?
In her comments, Mrs Trump said she "hates to see children separated from their families and hopes both sides of the aisle [Republicans and Democrats in Congress] can finally come together to achieve successful immigration reform".
"We need to be a country that follows all laws, but also a country that governs with heart," her statement added.
Laura Bush, wife of the former Republican President George W Bush, went further and launched an outspoken attack on the policy.
"This zero-tolerance policy is cruel. It is immoral. And it breaks my heart," she wrote in the Washington Post.
"Our government should not be in the business of warehousing children in converted box stores or making plans to place them in tent cities in the desert."
"These images are eerily reminiscent of the Japanese American internment camps of World War Two, now considered to have been one of the most shameful episodes in US history," she added.
'Super detention centre'
Mat Morrison, BBC News, Brownsville, Texas
If not for the security stations, boarded up windows, and barricades with 'KEEP OUT' painted clearly in black, this would look like any other Walmart on any given Sunday.
But this is the Casa Padre detention centre in Brownsville, Texas, and the visitors today are not afternoon shoppers, but a handful of US lawmakers who came to see for themselves the impact of the "zero-tolerance" immigration policy.
"They call it zero-tolerance, but a better name for it is zero-humanity. And there is zero logic to this," says Democratic Senator Jeff Merkley of Oregon, who organized the visit.
"What we saw is this huge warehouse, it was a super centre for Walmart before, now it's a super detention centre. It's holding almost 1,500 kids inside there."
"There are walls that have been constructed that go up near the ceiling, long corridors, because you need a lot of bedrooms, and they have some common space as well," he said.
Who is to blame?
Mr Trump has said a law "Democrats gave us" is responsible for the policy, but it is unclear which law he is referring to.
In a tweet on Saturday he urged Democrats to work with Republicans to create new legislation.
However, critics have pointed out that detaining children separately from their parents was a policy announced by US Attorney General Jeff Sessions last month and does not require congressional action to be stopped.
The significant change, analysts say, is the Justice Department's decision to criminally prosecute parents for a first-time border crossing offence. The children, however, are not charged with a crime, which means they cannot be jailed together.
What's happening now?
The recent child detentions - reportedly including babies and toddlers - have resulted in some shelters and foster homes reporting that they are running out of space.
On Sunday, Democratic members of Congress paid a "surprise Father's Day visit" to an Immigration and Customs Enforcement (ICE) detention centre in New Jersey, demanding to see detainees separated from their children.
Meanwhile, officials announced plans to erect tent cities that will hold hundreds more children in the Texas desert where temperatures regularly reach 40C (105F).
Local lawmaker Jose Rodriguez described the plan as "totally inhumane" and "outrageous", adding: "It should be condemned by anyone who has a moral sense of responsibility."
Protesters marched to one such tent city in Tornillo, Texas, on Sunday where hundreds of children were being held separately from their parents.
They chanted "Families united!" and "Free our children now!", reported NPR.
Is the policy working?
The number of families trying to enter the US overland without documentation is on the rise. Mr Sessions has recognised this, commenting last month that current immigration trends "must end".
In the first two weeks of the new "zero-tolerance" approach, 658 minors - including many babies and toddlers - were separated from the adults that travelled with them, according to US border officials.
In many of the cases, the families have been reunited after the parent was released from detention. However, there are reports of people being kept apart for weeks and even months.
But it is not clear if this new tougher policy will stop the migrants from travelling.
This is because many are fleeing violence and poverty in countries such as Honduras and El Salvador, and staying put is often fraught with dangers.
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