A US federal judge has ordered that families separated at the US-Mexico border must be reunited.

More than 2,000 children have been separated from their parents in the wake of the introduction of a 'zero tolerance' policy targeting illegal immigration.

While Donald Trump has signed an executive order to end the practice of family separation, many of the families affected have yet to be reunited.

The American Civil Liberties Union (ACLU) had taken legal action on behalf of two cases where parents had been separated from their children.

The Guardian reports that while those two families have now been reunited, the case has been expanded on behalf of other affected immigrants.

Overnight, California Judge Dana Sabraw ordered that all children under five must be reunited with their parents within 14 days, and older children within 30 days - and he also ordered officials to 'facilitate regular communication' between separated parents and children.

The preliminary injunction halts the practice of family separation, with the judge saying that the executive order to end the practice "is not absolute".

"Reactive governance"

Judge Sabraw writes: "The facts set forth before the Court portray reactive governance - responses to address a chaotic circumstance of the Government’s own making.

"They belie measured and ordered governance, which is central to the concept of due process enshrined in our Constitution. This is particularly so in the treatment of migrants, many of whom are asylum seekers and small children."

ACLU's Lee Gelernt welcomed the result as an 'enormous victory', saying: "Tears will be flowing in detention centers across the country when the families learn they will be reunited."

Separately, 17 American states are suing Donald Trump's administration over the separation of migrant families.

They want to force the government to reunite the thousands of immigrant children and parents it's previously divided at the southern US border.

New York Attorney General Barbara Underwood called the policy "inhumane, unconscionable, and illegal".

The latest developments come in the wake of the US Supreme Court decision to uphold President Trump's travel ban targeting a number of Muslim-majority countries - a significant victory for the administration.