Nearly 1,000 migrant children separated at the US-Mexico border by former US President Donald Trump’s administration have yet to be reunited with their parents, despite a two-year effort by President Joe Biden.

The US Department of Homeland Security said Thursday that of the 998 children still separated, 148 are in the process of being reunited.

Biden issued a presidential executive order shortly after taking office in January 2021 that established a task force to reunite children separated from their families under Trump, a hardline Republican on immigration, calling such separations a “human tragedy.”

The Trump administration has separated thousands of migrant families under a general “zero tolerance” policy that required the prosecution of all unauthorized border crossings in the spring of 2018.

The Department of Homeland Security said the task force’s meticulous work combing through “shredded” information held by the Trump administration on the policy so far has found 3,924 children, mostly Central Americans, separated at the border.

Many were located and assembled before Biden took office through a court case after the American Civil Liberties Union (ACLU) filed a lawsuit to stop the separation policy.

“The number of new families identified continues to increase as families come forward and identify themselves,” DHS said in a note about the task force’s work released Thursday. So far, the mutirão has brought together 600 families.