The American Civil Liberties Union has sued over the Trump administration's "zero-tolerance" family separation practice.

The children were expelled along with thousands of adults under new rules designed to slow the spread of coronavirus in the United States, according to court documents.

In court papers, the Trump administration argued a federal judge did not prove allegations that ICE isn't doing enough to control the spread of coronavirus in detention facilities.

Citing the recent spread of the virus in two of the three facilities, U.S. District Judge Dolly Gee set a deadline of July 17 for children to either be released with their parents or sent to family sponsors.

That’s more children detained away from their parents than any other country, according to United Nations researchers.

Children from that period can be difficult to find because the government had inadequate tracking systems.

So far, the only private company caring for migrant children held more than 20 per cent of all migrant children in government custody.

``We are burning up our future -- literally,'' Bachelet said. ``The world has never seen a threat to human rights of this scope. This is not a situation where any country, any institution, any policymaker can stand on the sidelines.''

A 1997 agreement known as the Flores settlement says immigrant children must be kept in the least restrictive setting and generally shouldn’t spend more than 20 days in detention.

The move is the latest effort by the administration to restrict immigration, U.S. President Donald Trump's signature issue.