The Trump administration separated thousands more migrant children from their parents than previously acknowledged, according to a report released Thursday.

Administration officials estimate that “thousands of separated children” entered the custody the Department of Health and Human Services in 2017 and into early 2018 even before President Donald Trump’s “zero tolerance” policy took effect, according to the department’s inspector general.

The separated children not previously disclosed were released prior to the June 26, 2018, order from a San Diego federal judge for the administration to reunify all separated families.

The department “was unable to provide a more precise estimate or specific information about these children’s placements” because “the tracking systems in use at that time were informal and designed for operational purposes rather than retrospective reporting.” Other government investigations have also noted that there was no centralized system to track children and parents who were separated by the government.

Staff at HHS’s Office of Refugee Resettlement began in the summer of 2017 to notice a “significant increase and proportion of separated children” among the population of unaccompanied minors they served, according to the investigators. There were some separations at the end of the Obama administration, in late 2016, when ORR staff informally estimated that about 0.3 percent of all intakes were separated children. By August 2017, they accounted for 3.6 percent of all intakes.

In a November 2017 email reviewed by investigators, an ORR official wrote that the children were often “very young” and required placement in specially licensed facilities but there are sometimes “shortfalls of available beds.’”