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

The U.S. Department of Homeland Security (DHS) said on Thursday of the 998 children still separated, 148 were in the process of reunification.

Biden, a Democrat, issued an executive order shortly after taking office in January 2021 that established a task force to reunite children separated from their families under Trump, a Republican and immigration hardliner, calling such separations a "human tragedy."

The Trump administration split apart thousands of migrant families under a blanket "zero-tolerance" policy that called for the prosecution of all unauthorized border crossers in spring 2018. Government watchdogs and advocates have found the separations began before and continued after the policy's official start.

DHS said the task force's painstaking work of combing through "patchwork" information kept by the Trump administration on the policy had so far found 3,924, mostly Central American, children were separated at the border.

Many were located and reunified before Biden took office through a court process after the American Civil Liberties Union (ACLU) sued to halt the separation policy.

"The number of new families identified continues to increase, as families come forward and identify themselves," DHS said in a fact sheet on the work of the task force released Thursday. To date the task force has reunited 600 families.

DHS also said it has connected some reunified families to services like access to mental health resources. Reuters in 2022 profiled a Honduran mother that ended up homeless for several months in the United States after she was reunited her with her young daughters that she had not seen in years.

Secretary Alejandro Mayorkas told reporters on Thursday that there was still work to be done to fully address wounds inflicted by the policy. "That's what informs our efforts to extend behavioral health services as a component of reunification," he said.