The Biden administration on Thursday pulled out of negotiations to offer financial compensation to thousands of migrant families for the harm inflicted on them by a Trump-era border policy that separated parents and children at the border.

Lawyers representing the families said that Justice Department lawyers had advised them that they were terminating negotiations to settle claims for damages and would instead go to court to determine any compensation due to individual families.

Talks had stalled, they said, after a leak in late October suggested that up to $450,000 could be paid to each of the families affected by the policy. The premature news, which was seized on by conservatives, complicated a nearly yearlong effort to compensate migrant families.

However, the lawyers said that they had not expected the administration to walk out of the discussions entirely. The policy, they have argued, was developed at the highest levels of government with the goal of deterring migrants who were seeking entry into the United States, often to claim protection from gang violence in their home countries.

“It’s shocking that the Biden administration would simply end negotiations without providing an opportunity for a settlement and would choose to defend this horrific practice publicly in court,” said Lee Gelernt of the American Civil Liberties Union, the lead counsel in the lawsuit that was brought to end the policy in 2018.

A Justice Department spokeswoman, Dena Iverson, said in a statement that while the parties had been “unable to reach a global settlement,” the administration remained “committed to engaging with the plaintiffs and to bringing justice to the victims of this abhorrent policy.”

Conservative leaders and commentators lambasted the administration for considering a large sum. Republicans, including some who had criticized the family separation policy, called the payments, or any payments, unwarranted.

Senator Mitch McConnell, the Republican minority leader, accused President Biden of wanting to “literally make millionaires out of people who have violated federal law.”

Mr. Biden said reports of the $450,000 maximum payment then under discussion were “garbage” when he was asked about it by a Fox News reporter. A few days later, he said that families should be compensated but that he did not know what amount might be appropriate.

“Obviously the Biden administration is caving to political pressure on immigration again instead of keeping its promise to do right by these families,” said Ann Garcia, a lawyer who represents several families subjected to the policy.

The family separations became emblematic of how far the Trump administration was willing to go to achieve its goal of halting the influx of migrants at the southwestern border.

In the spring of 2018, then Attorney General Jeff Sessions announced that the government would criminally prosecute everyone who crossed the border illegally, imprisoning parents and placing their children, some just months old, in shelters and foster homes across the country. This included families that had approached a port of entry to request asylum from persecution in their home countries, migrants who are supposed to have protection under the law.

The goal of the policy, officials said then, was to discourage the large number of Central American families that were making the perilous journey to the U.S. border, many of them fleeing violence in their countries.

Dr. Colleen Kraft, who was president of the American Academy of Pediatrics, said at the time that she was dismayed at the policy’s “sweeping cruelty.”

The separations were widely condemned not only by Democrats but also by some Republicans, including Senator Ted Cruz of Texas as well as Melania Trump and Laura Bush.

A federal judge in San Diego ordered the administration to reunify the families in June 2018, but by then many of the parents had been deported.

“This cruelty did not happen by accident,” said Mr. Gelernt, the A.C.L.U. lawyer. “Trump administration officials sat down and devised this as official U.S. policy, ordering that children be taken away day after day, no matter how young, some only 6 months old.”

All told, 5,500 families were identified as separated at the border, and Mr. Biden has promised to make amends for the “moral and national shame.”

Two distinct proceedings seeking to hold the government accountable for the policy have been unfolding this year, and the Biden administration had been trying to settle both.

In February, the White House established a task force to reunify families, consider giving them a pathway to remain in the United States and provide other assistance. Led by Alejandro Mayorkas, the secretary of the Department of Homeland Security, the task force has been in negotiations with the A.C.L.U. to settle a class-action lawsuit over the separations, to find and reunite families that remain separated, and to provide all the families a pathway to live in the United States permanently. Those talks continue.

In separate negotiations, lawyers representing separated families had been in discussions with Justice Department lawyers over financial compensation for the injuries caused by the policy. Hundreds of lawyers filed more than 900 claims against the government, but those settlement discussions have now been suspended with the Justice Department’s decision to go back to court, lawyers said.

In filings reviewed by the Times, the plaintiffs’ lawyers accuse the government of negligence, torture and crimes against humanity. The claims describe emotional and physical abuse that occurred during the separations and trauma that, in many cases, still lingers.

In one such case, a 19-month-old child could not remember his father when they were reunited, and then exhibited anger, irritability and withdrawal, according to the complaint. He had passed through three foster families. Some children were sexually molested by staff members in shelters, according to some filings; many families said their children still suffer from sleeplessness, nightmares and digestive issues.

Most of the families have been reunited. The locations of about 270 parents remain unknown.