In this June 12, 2018, file photo, US Border Patrol agents take a father and son from Honduras into custody near the U.S.-Mexico border outside Mission, Texas. The asylum seekers were then sent to a US Customs and Border Protection processing center for possible separation. US border authorities were executing the Trump administration's "zero tolerance" policy toward undocumented immigrants.
CNN  — 

The Trump administration separated more families along the US-Mexico border than was previously disclosed, according to a court document filed Wednesday.

The government has identified 1,556 children who officials believe were separated from their parents at the border between July 2017 and June 2018, adding to the more than 2,700 families who had been separated under the administration’s controversial “zero tolerance” immigration policy.

The latest review was prompted by an explosive government watchdog report in January that revealed there could be more separated families that officials hadn’t previously acknowledged. Officials estimated that “thousands of other children” were separated, received by the Health and Human Services Department for care and released prior to the June 26, 2018, court order that required the government to identify and reunify certain separated children.

Last year, a court order from US District Judge Dana Sabraw in San Diego forced the reunification of many immigrant families the government had separated at the border as a result of “zero tolerance.” Sabraw ruled in March that this group should be included in the class action lawsuit over family separations.

Over recent months, the government was tasked with combing through thousands of files to identify the children. Earlier this year, officials said they needed to review some 47,000 files dating back to July 1, 2017.

The government has since provided regular updates to the court and has described the cases identified in filings as children of “potential class members,” noting that the numbers could fluctuate as teams continued to analyze files and track down details about them.

The American Civil Liberties Union, which brought the case and received the final tally ahead of time, announced the government’s findings last month.

“It is shocking that 1,556 more families – including babies and toddlers – join the thousands of others already torn apart by this inhumane and illegal policy,” said Lee Gelernt, lead attorney in the family separation lawsuit and deputy director of the ACLU’s Immigrants’ Rights Project, in a statement. “Families have suffered tremendously, and some may never recover. The gravity of this situation cannot be overstated.”

The Trump administration implemented its “zero tolerance” policy from May 2018 to late June 2018. The policy called for the criminal prosecution of adults crossing the border, resulting in thousands of children being separated from their parents and placed in government care.

The Health and Human Services inspector general recently released a report detailing the toll the separations had taken on the children.

The report included accounts of facility staff detailing the inconsolable crying of children when they were separated, the kids’ confusion and their belief they had been abandoned by their parents.

As a result of the policy and longer stays in government custody, facility staff faced challenges in meeting the mental health needs of children, many of whom had already experienced significant trauma before arriving to the United States.

“Every single separated kid has been terrified. We’re (seen as) the enemy,” a program director says in the report, noting that separated children couldn’t tell the difference between facility staff and immigration agents.

In an interview at the FORTUNE Most Powerful Women Summit last month, former Homeland Security Secretary Kirstjen Nielsen was asked multiple times whether she regretted signing a memo that led to the separation of families.

She said, “I don’t regret enforcing the law, because I took an oath to do that.”

But added that she wished the coordination of the information flow had “worked a lot better.”

CNN’s Catherine Shoichet contributed to this report.