None of the hundreds of families separated as part of former President Trump’s zero-tolerance policy have been reunited by the Biden administration, Department of Homeland Security (DHS) officials told reporters on a call Wednesday. 

"Regarding the reunifications thus far, the task force has not directly reunified any families yet, and that's because we really are trying to build the processes and the information," a DHS official said. 

The officials said they are working "as quickly as we can" to identify parents and reunite children, despite a lack of information left by the Trump administration, but they are being meticulous "because we are very concerned about not retraumatizing" the children. 

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"There is also a lot of misinformation in the files - wrong dates, confusion in names, doubled up cases," the official said. "Those are just a few of the issues we are discovering."

President Biden campaigned on a promise to create a task force to reunite children with their parents who were separated at the southern border. He created the task force in early February.

The task force is now scouring the records of an additional 5,600 files of migrant children to see if they were separated from their parents. The effort is expected to uncover a small number of additional separations. 

In 2018, U.S. District Judge Dana Sabraw in San Diego, Calif., ordered the families be reunited. 

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The zero-tolerance policy stopped the practice of adults being admitted to the U.S. when claiming asylum if they were accompanying a child. Due to court orders preventing minors from being held in detention for more than a few weeks, it meant that children were placed in care or transferred to relatives in the U.S., while parents or guardians were deported. 

Thousands of children were separated at the border, and Trump withdrew the policy after a bitter backlash. The American Civil Liberties Union (ACLU) identified 4,000 children who were separated under the zero-tolerance policy. Parties in the ACLU lawsuit have been unable to reach the parents of about 500 children subject to the Trump-era separations.

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Lee Gelernt, the lead ACLU attorney in the litigation, said on Wednesday his organization does not know how many children remain separated from parents but that he believed it was likely more than 1,000.

The Associated Press contributed to this report.