Hundreds of parents who were separated from their kids at the U.S.-Mexico border remain "unreachable"

Advocates have been unable to reach the parents of 545 children who were separated by U.S.

These parents, designated as "unreachable" in Tuesday's court filing, are part of more than 1,000 migrant families who were separated by U.S.

when the ruling was issued were eventually reunited, but Sabraw authorized a steering committee of advocacy groups to track down the hundreds of parents who were deported without their children.

government revealed it had separated an additional 1,556 children from their parents between the summer of 2017 and June 2018, including during a pilot program for the "zero tolerance" policy in El Paso, Texas.

So far, the committee has located the parents of 485 of these children, but continues to look for the parents of 545 minors, two-thirds of whom are believed to have been deported to their home countries.

It is unclear how many of the "unreachable" parents have not yet reunited with their children after their forced separations in the U.S.

"Sadly we are still looking for hundreds of families who were separated years ago and will not stop until we find all of them," Lee Gelernt, the top ACLU attorney in the case, told CBS News