Judge requests list of migrant children who remain separated from their families by Saturday

The Department of Justice on Friday asked a federal judge for more time to reunite families separated at the U.S.-Mexico border as a result of the Trump Administration's "zero-tolerance" immigration policy.

Lawyers for the agency argued that meeting an upcoming July 10 court-mandated deadline to reunite children under age 5 and a subsequent deadline to reunite the nearly 3,000 remaining children later this month would be difficult.

In a hearing late Friday afternoon, the judge requested a case-by-case list from the government by Saturday, 5 p.m. PT, of around 100 children under 5 who still need to be reunified with their parents, and on Monday morning will rule if a reunification deadline can be extended for some of those cases.

One of the biggest challenges: ensuring parents are properly verified.

The lawyers previously informed the court they may not be able to comply with the court-ordered timeline for reunification because some families may no longer in government custody, due to parole or release -- which then extends the time needed to vet the parent to ensure parentage and child safety.

In Friday's legal request the government asked for more time and clarification on if their current process for confirming parentage is consistent with the court's mandate and "seeks clarification that in cases where parentage cannot be confirmed quickly, HHS will not be in violation of the Court’s order if reunification occurs outside of the timelines provided by the Court."

On Thursday, Department of Health and Human Services Secretary Alex Azar told reporters the agency will be in compliance with the court-ordered deadline of July 10 for those under 5, even if it means “HHS also had to narrow its traditional focus from the review of care” to a “more expeditious process” of vetting than the agency typically undertakes. And we're using DNA testing to confirm parentage quickly and “proper and careful vetting for child safety.”

Lawyers acknowledged on Friday that, "Although HHS is moving expeditiously to undertake these DNA tests, that process takes meaningful time, even when it is expedited—as this Court has implicitly recognized," the court documents said.

Government attorneys were apprehensive to provide specific names or cases and preferred to get an extension for the class as a whole. They cited unique or peripheral cases that have special circumstances that could make reunification by Tuesday's deadline difficult.

Some of the more difficult scenarios included 16 children who have not been matched to parents and an estimated 19 additional children whose parents have been released from custody with their whereabouts unknown. There are also cases where children have non-biological parents who cannot be matched through DNA.

American Civil Liberties Union attorneys offered to facilitate a public-private partnership to allow lawyers to help the government locate parents released from custody to help speed along reunification.

The government is concerned with meeting the deadline while also ensuring protocols laid out in the Trafficking Victims Protection Reauthorization Act (TVPRA), and wanted the courts guidance on if TVPRA protocols should be waived in order to meet the Tuesday deadline -- or if the protocols were more important and if the timeline should be modified.

ABC News' Matt Fuhrman, Elissa Stohler and Sunny Antrim contributed to this report.