House Reps. Joaquin Castro of Texas and Ilhan Omar of Minnesota will be among a group of Democrats traveling to observe conditions at an immigration facility for unaccompanied migrant children later this week amid concerns about a mounting crisis at the southern border.

Castro tweeted Monday that he was organizing a "delegation" of House Democrats to make the trip to the border. More than 15,000 unaccompanied migrant minors are reportedly in custody at federal facilities, according to CBS News.

"On Friday, I’ll lead a delegation to the Carrizo Springs facility for unaccompanied children at the border — oversight to ensure humane treatment and orderly process to unite kids with families," Castro wrote on Twitter. "For any member of Congress who would like to attend, please reach out to my office."

"I'll be there," Omar wrote in response.

U.S. Customs and Border Protection reported encounters with more than 100,000 migrants in February alone. Republican critics of the Biden administration have argued the president’s decision to reverse several Trump-era policies, such pulling funding for the border and loosening restrictions for asylum claimants, have exacerbated the crisis.

Omar was an outspoken critic of Trump’s immigration policies. Her website refers to current U.S. immigration law as "fundamentally unjust and tragically inhumane."

"The right to seek asylum is guaranteed under U.S. and international law," Omar tweeted. "Stop falling for Republican talking points and show some humanity!"

Castro visited the border to observe conditions at immigration facilities several times in recent years. In July 2019, he and fellow Rep. Alexandria Ocasio-Cortez were part of a delegation that toured facilities near Texas’ southern border.

At the time, Ocasio-Cortez described conditions at the detention facilities as "horrifying." It’s unclear if she plans to attend the upcoming trip with Castro.

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Prominent Republicans have pressed the Biden administration to refer to the border situation as a "crisis" and reverse course on key policy measures. Biden told reporters Sunday that he plans to visit the southern border "at some point" but did not provide further details.

When asked Monday if she planned to visit the border, Vice President Kamala Harris responded, "not today." She later indicated that she would likely visit in the future.