Democrats called for a swift investigation after federal immigration authorities confirmed on Thursday that a 7-year-old girl from Guatemala died of dehydration and shock hours after being taken into custody by the U.S. Border Patrol last week.

Rep. Jerry Nadler, D-N.Y., said on Twitter Thursday evening that he will be demanding "immediate answers to this tragedy" from Department of Homeland Security Sec. Kirstjen Nielsen, who is slated to testify before the House Judiciary Committee next week.

A 7-year-old child dies while in the custody of the U.S. government. ⁦@DHSgov⁩ Secretary is coming before ⁦@HouseJudiciary⁩ next week, and we will be demanding immediate answers to this tragedy. https://t.co/5XCAavD5wB — (((Rep. Nadler))) (@RepJerryNadler) December 14, 2018

Nadler, who is currently the ranking member of the House Judiciary Committee, is expected to be its chair when the new Congress convenes in January.

The Washington Post reported on Thursday that the girl and her father were part of a group of 163 people who approached U.S. agents to turn themselves in at the border. They were then taken into custody around 10 p.m. on Dec. 6 in New Mexico.

Customs and Border Protection said in a statement that more than eight hours later, the child began having seizures. Emergency respondents recorded a body temperature of 105.7 degrees and, according to The Washington Post, the girl apparently had not eaten or drunk water for several days.

Sen. Richard Blumenthal, D-Conn., a member of the Senate Judiciary Committee, said the story "shocks the conscience" and said he will be "demanding answers."

"This senseless tragic death shocks the conscience. Immediate investigation must shine a spotlight on people & practices responsible," Blumenthal said on Twitter Friday.

"Why did the Commissioner of Customs & Border Protection keep this little girl’s death secret until after he testified before me & Senate Judiciary Committee this week? I will be demanding answers," Blumenthal continued.

Rep. Pramila Jayapal, D-Wash., who also sits on the House Judiciary Committee, also called for an investigation, and said Congress should cut off funds to agencies where children die in custody.

Nielsen "has this on her hands," Jayapal said on Twitter, adding that if "'border security' means detaining 7 year old children and letting them die in OUR custody, SHAME ON US. No more money without accountability."

The DHS secretary told Fox News on Friday that the migrant girl's death is “a very sad example of the dangers of this journey,” and stressed that the girl's family "chose to cross illegally."

In a statement on Friday, the agency offered condolences to girl's family, but echoed Nielsen's remarks about the hazards of crossing the border.

"Unfortunately, despite our best efforts and the best efforts of the medical team treating the child, we were unable to stop this tragedy from occurring. Once again, we are begging parents to not put themselves or their children at risk attempting to enter illegally. Please present yourselves at a port of entry and seek to enter legally and safely," a spokesperson said.