HOUSTON (AP) — Immigration advocates accused the U.S. government on Thursday of “effectively disappearing” hundreds of children in a complaint over the widespread separation of families crossing the southern border.

The groups filed a petition with the Inter-American Commission on Human Rights, which investigates alleged human rights abuses in North and South America.

Attorney General Jeff Sessions announced May 7 that the Justice Department would begin to prosecute every person accused of illegally crossing the U.S.-Mexico border. Hundreds of families have been separated since then. An official from U.S. Customs and Border Protection recently told Congress that 638 adults had been referred for prosecution between May 6 and May 19, bringing with them 658 children.

ADVERTISEMENT

By comparison, the U.S. Department of Health and Human Services, which shelters unaccompanied immigrant children, said in April that it had approximately 700 cases since October in which the parents were believed to be in federal custody.

Immigration lawyers and advocates say parents are being held in jail without knowing where their children are.

Efren Olivares, a lawyer with the Texas Civil Rights Project, which filed the complaint, said the U.S. government’s separating of families is “clearly in violation of international law.”

“No developed democracy in the world separates children and parents just because they came into the country,” he said.

The Women’s Refugee Commission and the University of Texas School of Law’s immigration clinic also joined the complaint.

In one case outlined in the complaint, Border Patrol agents in South Texas arrested a 40-year-old man from Guatemala with his 12-year-old son. The complaint says the man was placed in a detention cell while his son was kept outside. By the time the man was taken out of the cell, the boy was gone.

A lawyer working on the man’s case called the government hotline for locating immigrant children in custody. According to the complaint, the boy’s information was not in the system. The lawyer and the father don’t know where he is.

Advocates say they hope the complaint will lead the Inter-American Commission on Human Rights to ask the government for more information about how it’s keeping track of families after separating them. The American Civil Liberties Union has also filed a federal lawsuit challenging family separation.

ADVERTISEMENT

U.S. Immigration and Customs Enforcement said in a statement that it is “committed to connecting these family members as quickly as possible after separation,” and that it will work with the Department of Health and Human Services to “set up regular communication and removal coordination, if necessary.”

Neither Health and Human Services nor Customs and Border Protection responded to requests for comment.