Homeland Security Secretary Kirstjen Nielsen on Wednesday testified that the government does not use "cages" to hold children as Democrats interrogated her about the Trump administration's practice of separating migrant families caught crossing the border illegally.

Nielsen and House Homeland Security Committee Chairman Bennie Thompson (D-Miss.) sparred at one point over the conditions used to detain migrant children and whether the government still uses cages to hold them.

"Sir, we don't use cages for children," Nielsen said, telling Thompson that the border facilities that he's visited were not intended to detain children.

"To my knowledge, [Customs and Border Protection] never purposefully put a child in a cage if you mean a cage like this," Nielsen added, making the shape of a box with her hands.

"Purposefully or whatever, are we putting children in cages as of today?" Thompson asked.

"They're not cages," Nielsen responded, calling them "areas of the border facility that are carved out for the safety and protection of those that remain there while they're being processed."

"We're not going to go through the semantics," Thompson said. "Now, I saw the ... fences that were made as cages. And you did, too. If it's a bad policy then change it, but don't mislead the committee."

The Trump administration last year enacted a policy that led to the separation of hundreds migrant families that illegally crossed the southern border. The move sparked widespread outrage, with Democrats seizing on images of children being detained in what appeared to be metal cages.

Nielsen on Wednesday defended the Trump administration's policies amid fierce questioning from Democrats over officials' handling of the family separations.