(CNN) — Lawyers have not been able to reach the parents of 545 children who had been separated from their families by US border officials between 2017 and 2018, according to a Tuesday court filing.

Hundreds of parents may also have been deported without their children.

The filing from the Justice Department and the American Civil Liberties Union is part of an ongoing effort to identify and reunite families separated by the Trump administration, more than two years after the “zero tolerance” policy was created.

While a federal court order forced the reunification of many of those families, an explosive government watchdog report released last year revealed there could be thousands more who hadn’t previously been acknowledged by officials.

A court-appointed “steering committee” has tried to locate those families. As of October 20, the committee has attempted to reach the families of 1,030 children. Of those, the committee has not been able to reach the separated parents of 545 children, according to the court filing.

“Approximately two-thirds” of parents are believed to have been deported without their children, the filing adds.

The children were previously released from government custody and almost all are likely in the United States with a sponsor.

While Covid-19 has hampered reunification efforts, the filing says, attorneys have resumed on-the-ground attempts to locate families.

“Following a suspension due to the COVID-19 pandemic, limited physical on-the-ground searches for separated parents has now resumed where possible to do so while protecting the health of personnel working with the Steering Committee and members of vulnerable communities in separated parents’ home countries,” the filing reads.

“Even before Covid, it was hard enough finding these families but we will not stop until we’ve found every one,” said ACLU attorney Lee Gelernt. “Some of these children have been separated for years and were just babies at the time.”

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