Republicans are demanding answers over reports of alleged child abuse at a migrant facility in Texas -- while renewing calls for the Biden administration to act to solve the crisis at the southern border they say is fueling it.

"The allegations of horrific abuse of children in the custody of the Biden administration are tragic," Sen. Ted Cruz, R-Texas, said in a statement to Fox News on Thursday. "We need to immediately get to the bottom of what is happening to these children and President Biden needs to step up and address the driving factor behind this -- his crisis at the southern border."

MORE THAN 1,300 MIGRANTS CHILDREN BEING HELD AT COLISEUM WHERE SEXUAL ABUSE IS ALLEGED 

Texas welfare officials said on Wednesday they received three reports of abuse and neglect at the Freeman Coliseum in San Antonio, Texas. The site holds more than 1,300 migrant children -- one of a number of sites set up to handle a surge in migrants in recent months.

Gov. Greg Abbott said he believed the allegations came from someone inside the facility and that they include sexual abuse, insufficient staffing, children not eating and COVID-positive migrants not being separated. 

Abbott, a Republican, called on the Biden administration to shut the site.

"The Biden administration opened the borders and failed to plan for the influx of unaccompanied children crossing the border, and now we are faced with our worst fears -- allegations of child abuse and neglect," he said. 

The Department of Health and Human Services (HHS) said in a statement to The Associated Press that it could not comment on specific cases but "has a zero-tolerance policy for all forms of sexual abuse, sexual harassment, and inappropriate sexual behavior."

Sen. John Cornyn, R-Texas, later called for an investigation into the allegations.

BIDEN ADMINISTRATION ANNOUNCES SKY-HIGH BORDER NUMBERS, LOOKS TO BLAME TRUMP

"The fact that any child would experience abuse in the care of the U.S. government is despicable," Cornyn said. "The HHS Inspector General must fully investigate these allegations and the treatment of children at this facility."

Cornyn has visited four migrant facilities housing unaccompanied minors in recent days and said he plans to visit a fifth this week.

Sen. Rob Portman, R-Ohio, said he was "deeply troubled" by reports that the Biden administration is removing protections for unaccompanied children to place them with sponsors and by  "reports of sexual abuse of those children at holding facilities." 

"Since 2015, my bipartisan oversight has shown, over two administrations, that federal agencies must do a better job of ensuring the safety and security of these vulnerable children," he said.

INSIDE THE BORDER CRISIS: PRESS TOURS PACKED TEXAS FACILITY WITH 4,000+ MIGRANTS 

There are currently more than 16,000 unaccompanied children in HHS care and more than 4,000 in Customs and Border Protection (CBP) custody. On Thursday, CBP announced there had been 172,000 migrant encounters in March. That included 18,890 unaccompanied children -- a 100% increase from the already high numbers encountered in February, and the highest monthly number recorded.

The Biden administration can expel single adults and some migrant families with Title 42 public health protections set up during the Trump administration but has chosen not to attempt to do so for unaccompanied children. 

Republicans have been increasing pressure on the administration to change course, and have blamed Biden’s reversal of Trump-era policies for the surge.

Biden officials have blamed the Trump administration for the surge, saying it did not do enough to increase bed space. Meanwhile, HHS has been ramping up efforts to increase capacity, including by requesting the use of military bases.

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In the last two months, HHS has opened multiple sites in areas like Carrizo Springs, Texas, and the San Diego Convention Center. Meanwhile, it has requested Pentagon approval for the use of three military bases in California and Texas.

Fox News' Ronn Blitzer, Michael Ruiz and The Associated Press contributed to this report.