McALLEN — A Mexican immigrant separated from her 10-year-old daughter with Down syndrome is being detained as a witness in a smuggling case, U.S. officials said Wednesday.

As outrage mounted about the Trump administration's zero-tolerance policy, officials issued the statement after Mexico's Foreign Affairs Secretary Luis Videgaray put a spotlight on the family's case at a news conference Tuesday.

He told reporters that the girl and her 10-year-old brother were being held at a facility in McAllen while their mother had been sent to a detention center in Brownsville.

.@Zac_Petkanas says on Fox News a 10-year-old girl with Down Syndrome was separated from her mother at the border.



Corey Lewandowski responds: "Womp womp." pic.twitter.com/cZMXWmwbjw — Jon Passantino (@passantino) June 19, 2018

But authorities with U.S. Customs and Border Protection said the separation happened because of the mother's role as a "material witness," not because she was being charged with illegal entry under the zero-tolerance policy.

The girl's plight became nationally known after former Trump campaign manager Corey Lewandowski responded "womp womp" on Tuesday on Fox News when former senior Democratic National Committee adviser Zac Petkanas said the child had been "taken from her mother and put in a cage."

Lewandowski on Wednesday tweeted that he "mocked a liberal who attempted to politicize children as opposed to discussing the real issue, which is fixing a broken immigration system." He also incorrectly said that Obama began the policy of separating minors from their parents when they enter the country illegally. The policy began under Trump.

The woman and her five children were traveling in a vehicle driven by a U.S. citizen. The mother admitted to being in the country illegally, Customs and Border Protection said Wednesday.

"This smuggler has a criminal history including a flight, escape, aiding and abetting, making it important that we prosecute," the agency's statement reads.

Lots of Fake News today. I mocked a liberal who attempted to politicize children as opposed to discussing the real issue which is fixing a broken immigration system. It’s offenseive that the MSM doesn’t want to talk about the fact these policies were started under Obama. — Corey R. Lewandowski (@CLewandowski_) June 20, 2018

Three of the woman's children are U.S. citizens and were released to an aunt, according to the statement.

The Mexican consulate in McAllen contacted the girl's father, who is a U.S. resident, and is working to reunite them, Videgaray said Tuesday.

Eduardo Bernal, the Mexican consul in McAllen, was not in his office when reporters visited Tuesday and Wednesday. An aide said he was tending to immigrants at a Border Patrol center.

In response to the Customs and Border Protection statement, Mexican officials issued their own, urging the U.S. government to reunite the children with their mother immediately.

Staff writer Jennifer Emily in Dallas contributed to this report.