Media playback is unsupported on your device Media caption Veronica is terrified she'll be separated from her daughter when she seeks asylum at the US border

The US government has asked for more time to reunite migrant families separated at the US-Mexico border as it emerged that some children's parents have already been deported.

In a two-hour hearing on Friday, a government attorney said that 19 parents of children under the age of five held in custody had left the US.

The justice department has a deadline to release these children by 10 July.

But it says that more time is needed to perform the necessary identity checks.

On Thursday, the US Department of Justice issued a formal request to Judge Dana Sabraw, a federal judge in San Diego, for relief regarding the earlier court order to release 101 children aged five and under by next Tuesday.

The judge, who has yet to rule on the extension, said the government needed to provide a full list of those under five held in custody by Saturday afternoon, following which the original deadline would be re-evaluated.

He also said the government would need to present expectations for meeting the deadline for each child on the list to the American Civil Liberties Union, which brought the class action lawsuit.

Judge Sabraw also scheduled a status hearing on Monday morning, saying he hopes an agreement can be reached regarding whether Tuesday's deadline will need to be extended.

The court order also includes a deadline to release children aged between five and 17 by 26 July.

During the hearing on Friday, the government attorney also provided an overview of the families affected. This included the following information:

16 children have not yet been matched to parents

19 parents have already been released into the US

46 parents are being held in custody by Immigration and Customs Enforcement (ICE)

Two parents have been judged unfit for release

Earlier this week, the US Department of Health and Human Services (HHS) said it had ordered DNA tests on some 3,000 children in an effort to reunite migrant families.

However, the justice department said that even while the health department was "moving expeditiously" with the tests, the process was time consuming.

It added that given the possibility of false claims, "confirming parentage is critical to ensure that children are returned to their parents, not to potential traffickers".

The government also needed to determine whether the adults had a criminal history or could present a danger to their children, the department said.

The US government did not request a specific new set of deadlines.

More than 2,300 migrant children have been separated from their parents since early May under the Trump administration's controversial policy, which seeks to criminally prosecute anyone crossing the border illegally.