The parents of 545 migrant children who were separated under US border policy cannot be found, a court filing and US rights group has revealed.
The separations were carried out in relation to US President Donald Trump's "zero tolerance" policy toward migrants who illegally crossed the border.
"Through our litigation, we just reported to the court that the parents of 545 kids — forcibly separated by the Trump administration's cruel family separation practice — still cannot be found," the American Civil Liberties Union tweeted.
"We won't stop until we have found every one of the families, no matter how long it takes."
Under the zero tolerance program, the US began separating children from their parents in May 2018, prompting a domestic and international outcry.
Then, six weeks into the practice Mr Trump announced that his administration would stop separating families unless the parents posed "a risk" to their child.
Two-thirds of the parents who cannot be found are believed to have been deported, according to a court document posted online by CNN.
According to NBC News, the children whose mothers and fathers have yet to be located were separated under a 2017 pilot program ahead of the zero tolerance policy, and were deported.
"It is critical to find out as much as possible about who was responsible for this horrific practice while not losing sight of the fact that hundreds of families have still not been found and remain separated," Lee Gelernt, deputy director of the ACLU Immigrants' Rights Project told NBC.
"There is so much more work to be done to find these families."
The global coronavirus pandemic briefly hampered a search for the children's parents, but has now resumed.
"Following a suspension due to the COVID-19 pandemic, limited physical on-the-ground searches for separated parents has now resumed where possible to do so while protecting the health of personnel," the court filing said.
News of the lack of success in finding so many parents was met with horrified reactions on social media on Wednesday, with people describing the situation as inhumane, unfathomable and cruel.
A 2018 court order mandated that the government reunite the separated families.
A report the total number of children separated from their parents remained unknown, but the US Department of Health and Human Services had identified 2,737 separated children put in its care before the zero tolerance policy was declared over.
