(CNN) A federal judge called the Trump administration's slowness to track down migrant parents it had separated from their children and then deported "unacceptable," saying the responsibility is "100%" on the government.

The stern admonishment from District Judge Dana Sabraw came a day after the administration argued that immigrant advocacy groups -- not the government -- should be responsible for tracking down the more than 500 parents it had separated from their children at the border and deported without them.

Sabraw said during a Friday phone hearing that if the government doesn't track down the parents, it will have "permanently orphaned" their children.

"The reality is there are still close to 500 parents that have not been located, many of these parents were removed from the country without their child, all of this is the result of the government's separation and then inability and failure to track and reunite," Sabraw said.

"And the reality is that for every parent who is not located, there will be a permanent orphaned child, and that is 100% the responsibility of the administration," he added.

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