WASHINGTON — For nearly three months this summer, the Obama administration carefully avoided answering questions about what happened to tens of thousands of immigrant families caught illegally crossing the Mexican border and released into the United States with instructions to report back to immigration authorities.

Homeland Security Secretary Jeh Johnson and others said they faced deportation. But it turns out that tens of thousands of those immigrants did not follow the government’s instructions to meet with federal immigration agents within 15 days. Instead, they have vanished into the interior of the U.S.

The Homeland Security Department privately acknowledged that about 70 percent of immigrant families failed to report as ordered. The disclosure came during a confidential meeting at its Washington headquarters with immigration advocates participating in a federal working group on detention and enforcement policies.

The Associated Press obtained an audio recording of Wednesday’s meeting and separately interviewed participants.

On the recording, the government did not specify the total number of families released into the U.S. since October. Since only a few hundred families have already been returned to their home countries and limited U.S. detention facilities can house only about 1,200 family members, the 70 percent figure suggests the government released roughly 41,000 members of immigrant families who subsequently failed to appear at federal immigration offices.

The official, who was not identified by name on the recording, also said final deportation had been ordered for at least 860 people traveling as families caught at the border since May but only 14 people had reported as ordered.

The Homeland Security Department did not dispute the authenticity of the recording.

In an emailed statement Thursday, Immigration and Customs Enforcement spokeswoman Gillian Christensen said the no-show figure represented “an approximate snapshot” of cases since May. Christiansen said some people may still report to immigration court hearings, and a “significant” number of deportation cases are still pending before judges.