Progressive lawmakers grilled a top Trump administration official Thursday about family separations at the border, with one member of the so-called "squad" accusing him of wanting to prolong the detention of children, which he denied.

Rep. Rashida Tlaib, D-Mich., at a House Oversight Committee hearing, accused Acting Homeland Security Secretary Kevin McAleenan and fellow administration officials of trying to change the long-standing agreement known as the Flores settlement that governs how immigrant children can be detained, "to keep kids longer" in custody. "Just admit that though - you want to keep the kids longer."

McAleenan explained that he wanted to keep families together for the time necessary it takes for immigration proceedings to go through, and for the justice system to make a ruling on the case. "We don't want to change the provisions about conditions in our custody. We want to codify those provisions to maintain the highest possible standard."

He added, "We want to keep families together through an immigration proceeding that's fair and expeditious in an appropriate setting. That can't be done in 20 days with due process."

Democrats have slammed the detentions as "inhumane," while many Republicans have accused the Democrats of hypocrisy, saying they were silent about similar detentions under the Obama administration.

McAleenan said fewer than 1,000 children have been separated from families out of 450,000 family groups that have crossed the border since October. He said they were separated because of health and safety concerns, among other reasons. "The vast majority" of families remained together, he said.

That tally did not include children who came with older siblings, or aunts and uncles and grandparents separated under longstanding policy meant to guard against human trafficking. McAleenan said Congress would need to amend laws to allow border officers more discretion in order to keep those groups together.

"As I have testified and warned publicly, dozens of times this year and last, we are facing an unprecedented crisis at the border," McAleenan told the committee.

U.S. Customs and Border Protection officials have encountered more than 800,000 migrants crossing the border from Mexico. Over 450,000 were families.

"Combined, that means over 300,000 children have entered our custody since October 1st," he said.

DHS CHIEF REVEALS STARTLING STAT ON ASYLUM SEEKERS WHO SKIP HEARINGS, DISAPPEAR

Rep. Alexandria Ocasio-Cortez, D-N.Y., questioned McAleenan about a series of controversial Facebook posts attributed to some Customs and Border Protection employees. Some of the posts included graphic, doctored images of the New York Democrat.

Ocasio-Cortez asked whether the agents were still on duty and wondered whether the family separation policy had contributed to a “dehumanizing culture.”

CLICK HERE TO GET THE FOX NEWS APP

McAleenan said some had been placed on administrative duty but didn’t elaborate.

“We do not have a dehumanizing culture,” McAleenan responded.

The Associated Press contributed to this report.