Migrant children separated from their parents at the border still haven't been reunited with their families.

According to NBC News, lawyers are working to get migrant children back to their families after the "zero tolerance policy" at the border.

But they were unable to make contact with the parents of some 666 children, deeming them "unreachable." The number is higher than the 545 migrant children they reported last month.

New York Times said in a report that the wide-ranging campaign to track down the parents go back to cases beginning in 2017.

Documents initially showed about 60 of the children were under the age of five when they were torn away from their parents.

But NBC noted that as per the most recent count, nearly 20% of the children faced this scenario. That's about double of the first record.

Lawyers for Migrant Child Ask for Government Assistance

Steven Herzog who was leading the reunion efforts explained the increase in an email to the Department of Justice.

He said the number grew because it now includes those "for whom the government did not provide any phone number," reported The Hill.

He also told DOJ attorneys that he would "appreciate the government providing any available updated contact information."

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If that can't be provided, any information that could help in establishing contact for all 666 parents will also do.

Lee Gelernt, deputy director of the ACLU Immigrants' Rights Project, also told the news organization that the new number includes cases without information from government that could lead to meaningful searches.

Gelernt said they were hoping the government could help them with the information they needed.

The Department of Homeland Security and the Department of Justice did not offer immediate comment.

"Zero Tolerance" Separated Migrant Children at Border

The "zero tolerance" policy was in effect from April to June 2018.

It separated migrant children from their undocumented parents on the US/Mexico border.

Before this policy at the border, the government also ran a pilot program testing family separation at the El Paso sector.

According to NBC News, most of the children whose parents can't be found were separated during this pilot program.

A court-ordered accounting of the separated families was first provided by the Trump administration in June 2018.

It dated back to the time where about 2,700 children were taken from their parents after crossing into the U.S.

The search involved many players including a private law firm and several immigrant advocacy organizations.

Some families may have been eventually reunited but in January 2019, the Health and Human Services Department's Office of Inspector General confirmed that more children were in fact separated.

In October 2019, the steering committee said it was able to locate parents of 485 children. The rest have not yet been found.

Read also: Joe Biden Plans to Reverse Trump's Immigration Policies Once He's in Office

President-elect Joe Biden promised to create a task force that will reunite the children and their parents.

As for whether the parents will be permitted to come to the country and ask for asylum, two sources said Biden has not decided on the matter yet.

The new findings highlight the lasting effect of the "zero tolerance" policy.

As the data confirmed, hundreds of families endured years of separation.