WASHINGTON (Reuters) - The U.S. government is moving some migrant parents to detention sites closer to the young children they were separated from while crossing the U.S.-Mexico border in an attempt to meet a court-imposed deadline to reunify families, U.S. Secretary of Health and Human Services Alex Azar said on Thursday.

U.S. Judge Dana Sabraw in San Diego last month ordered the government to stop separating children from immigrant parents entering the United States illegally and set deadlines for the government to reunite families.

The judge’s order followed a political firestorm over U.S. President Donald Trump’s “zero tolerance” immigration policy and beefed up efforts to deter illegal U.S. entry.

Sabraw set a deadline for children under 5 years old to be reunited with their parents by July 10, and for all children to be reunited by July 26. He also set a deadline of Friday for parents to be in phone contact with their children.

Azar said that based on a comprehensive audit by HHS and immigration authorities, there were now fewer than 3,000 children in HHS care who may have been separated from parents taken into custody for crossing the border illegally or for other reasons, such as concern over safety of the child.

Of that group, approximately 100 children are under the age of 5, he said.

To speed the reunification process, the Department of Homeland Security is relocating parents of children under 5 years old to detention facilities close to their children “so that we can as expeditiously as possible reunite the children with their parents to meet the court’s deadline,” Azar said.

No children have yet been reunified with parents in the custody of Immigration and Customs Enforcement, but that will soon happen to meet the court deadline, Azar said.

He added, however, that deadlines imposed by the court will require a “truncated vetting process” and that the government will likely “seek additional time to ensure that we can do the job that we believe is necessary to protect the children in our care.”

FILE PHOTO: Immigrant children, many of whom have been separated from their parents under a new "zero tolerance" policy by the Trump administration, are being housed in tents next to the Mexican border in Tornillo, Texas, U.S., June 18, 2018. REUTERS/Mike Blake/File Photo

Government personnel are currently collecting cheek swab DNA samples from parents and children in order to verify family relationships, said Jonathan White, deputy director for children’s programs at the Office of Refugee Resettlement, the HHS office that takes care of the children.

White described the DNA process as faster than verifying relationships through documents such as birth certificates.

“We have to protect children from people who would prey on them, and that is what we are doing,” he said. “These DNA results are being used solely for that purpose and no other.”

In a reversal last month, after family separations at the border triggered a groundswell of opposition, Trump ordered that detained migrant families be kept together if possible.

In the past, families detained while crossing the U.S.-Mexico border were often released from custody to pursue their immigration cases while living freely in the United States, but the Trump administration has made clear that it intends to end what it derides as “catch and release” immigration policies.

A 1997 court ruling known as the Flores settlement has been interpreted to prevent detention of children for more than 20 days, which is one reason the administration gave for its policy of separating families when it decided to keep parents in custody.

Last month, the administration asked a federal court to modify the agreement so that it could detain children longer. It filed court papers last week saying it believed it had the right, under the current settlement, to hold children longer in order to enable family reunification and prevent future separations.

Lee Gelernt, deputy director of the ACLU’s Immigrants’ Rights Project, which filed a lawsuit challenging the family separations, questioned the government’s contention it might need more time to safely reunite families.

“When the government wants to marshal its resources to separate families, it has shown that it can do it quickly and efficiently, but when told to reunite families, it somehow finds it too difficult and cumbersome to accomplish,” he said.

Wendy Young, president of Kids in Need of Defense, said her organization, which provides legal assistance to unaccompanied minors, was unaware of any comprehensive government plan for uniting families.

One test will be if the government can meet Friday’s deadline to get parents in touch with their children by phone, she said.

“If they fail to meet that deadline, I think it calls into serious question whether they will be able to meet the reunification deadlines in the coming weeks,” Young said.