What happens to the children?
According to a Department of Homeland Security spokesman, between April 19 and May 31, 1995 children were separated from 1940 adults who were being held by US border patrol.
There is no information about the age of the children.
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Amid outcry over the detentions, a Department of Health and Human Services (DHS) spokesperson insisted the minors were held in decent conditions.
"We have some of the highest detention standards in the world for children," the spokesperson said.
There is no law that requires parents be separated from their children at the border - but if parents in the United States are jailed, their children are split from them because the children are not themselves charged with a crime.
The children are put into the care of the US Department of Health and Human Services, and some are transferred to government facilities or foster care during the separation.
More than one thousand boys are being held in a former Walmart supermarket in Texas, and the government is building tent structures near the border to house the increasing number of migrant children, including unaccompanied minors, in custody.
A DHS official refuted claims agents had separated a breastfeeding mother from her baby.
"We do not separate breastfeeding children from their parents, that does not exist, that is not policy," the spokesperson said.
The DHS official also rejected as "not true" various reports of wrongdoing, including the turning away of some asylum-seekers.
Political debate rages on
On Thursday, US Attorney General Jeff Sessions cited a biblical verse to support the 'zero tolerance' approach, and critics were quick to point out the same passage was once used to justify slavery.
"I would cite you to the Apostle Paul and his clear and wise command... to obey the laws of the government because God has ordained the government for his purposes," he said.
With the crackdown in full swing, the detained parents are "in jail settings," a DHS official said, awaiting adjudication and possible prosecution for crossing the border. The process can take several weeks.
"This administration has made it clear that we are not going to ignore the law any longer," the official said.
Meanwhile, congressional Republicans have struggled to craft a viable immigration plan - House Speaker Paul Ryan, who is the US Congress' highest-ranking Republican, said he is not comfortable with the approach that has been taken.
"We don't want kids to be separated from their parents," Mr Ryan said.
The Republican-led House of Representatives may vote next week on two immigration measures - a hard-line bill drafted by House Judiciary Chairman Bob Goodlatte, and a compromise measure that limits legal immigration while also ending the family separations.
"I'm looking at both of them," Donald Trump told Fox News.
"I certainly wouldn't sign the more moderate one."
Hours after Trump's comments, the White House issued a statement saying the president had misspoken.
"The president fully supports both the Goodlatte bill and the House leadership bill," according to White House spokesman Raj Shah.
'This is barbaric': Democrats slam the policy
The compromise House Republican bill reportedly would provide $25 billion for a border wall, and detail a process giving young undocumented immigrants permanent residency and a pathway to citizenship.
On Twitter, Trump addressed what he specifically wants in new legislation including "full funding for the Wall;" an end to a diversity visa lottery and certain categories of family-based migration; and a shift toward "merit-based immigration" for skilled workers.
The president directed the blame at the Democrats for "forcing the breakup of families at the border" because they are pushing their own "cruel" legislative agenda.
Democrats fired back, with top House Democrat Nancy Pelosi calling the Republican proposal "simply unworthy of America."
"This is barbaric. This is not what America is," she said.
Family separation "is an immoral, horrific policy," added Senator Dianne Feinstein, who has introduced legislation to keep immigrant families together.
- With AFP.