WASHINGTON — It seems likely that thousands more migrant children were split from their families than the Trump administration has acknowledged, in part because officials were stepping up family separations long before the border policy that prompted international outrage last spring, a government watchdog said Thursday.

It’s unclear just how many family separations occurred at the U.S.-Mexico border; immigration officials are allowed under longstanding policy to separate families under certain circumstances. Health and Human Services, the agency tasked with caring for migrant children, did not adequately track them until after a judge ruled that children must be reunited with their families, according to the report by the agency’s inspector general.

Ann Maxwell, assistant inspector general for evaluations, said the number of children removed from their parents was certainly larger than the 2,737 listed by the government in court documents. Those documents chronicled separations that took place as parents were criminally prosecuted for illegally entering the country under President Donald Trump’s “zero tolerance” policy.

“It’s certainly more,” Maxwell said. “But precisely how much more is unknown.”

Lee Gelernt, an American Civil Liberties Union attorney who sued on behalf of a mother separated from her son, said the separation policy “was a cruel disaster from the start. This report reaffirms that the government never had a clear picture of how many children it ripped from their parents.”