The Trump administration official in charge of caring for undocumented minors separated from their parents at the border said on Thursday that his agency must reunite nearly 3,000 families, a sharp increase from the roughly 2,300 his agency was contemplating as of last week.

Department of Health and Human Services Secretary Alex Azar said the work has been further complicated by the nation's "disjointed" immigration laws, the broad scope of the judge's "unprecedented" order, requests from members of Congress to tour HHS facilities, delays verifying familial relationships, and "unreliable" information provided by minors who are being held in detention.

But Azar insisted that his agency will fully comply with a ruling from District Judge Dana Sabrow to reunite all children separated from their parents under President Donald Trump's "zero-tolerance" policy by the end of this month. The judge ordered the department to reunite children under age 5 by Tuesday, and all minors by July 26.

"We will use every minute of time we have to confirm the parentage of those individuals … and to confirm that those parents are actually suitable for reunification, and then we will comply with the court’s order and reunify them," he said during a conference call with reporters. "We will comply with the artificial deadlines established by the courts."

The number of children in question has changed significantly in recent weeks.

In early June, U.S. Customs and Border Protection estimated that 2,342 children had been separated from their parents under the "zero tolerance" policy carried out the departments of Justice and Homeland Security. On June 20, Azar testified before Congress and said they had reunited several hundred families, leaving 2,053 children in HHS custody. On June 26, he testified again before Congress, saying the number had fallen to 2,047.

But on Thursday, Azar said his department was forced to examine the cases of all 11,800 minors in its custody because the judge ordered all children to be reunited with their parents, even those separated before the "zero tolerance" policy went into full effect in May.

Most of the cases, he said, were minors who crossed the border on their own. But he said close to 3,000 may have been separated, leading to the higher estimate. About 100 of them are under age 5, Azar said.

Now, his department is working case-by-case to ensure that each minor is indeed related to their purported parent. Azar said that can usually be accomplished by checking paperwork, such as birth certificates and consular documents. But he said that process can be slow, given the time it takes to secure official documents and the uncertainty of stories told by some kids.

He said some minors, for example, are labeled as separated from their parents. But when inspecting cases more closely, those parents had separated from their child before crossing the southwest border, meaning the U.S. government did not separate them and has no responsibility to reunite them.

To speed up the family verification process, Azar said his officials are doing DNA checks of all alleged parent-child relationships. That process has been used in the past when there were questions about familial relationships, so Azar said it was the best option given their time constraints.

A private contractor does a cheek swab of each person, then compares their DNA to verify the relationship. Jonathan White, assistant secretary for preparedness and response at HHS, said those tests are necessary to ensure that human traffickers posing as parents aren't reunited with children.

"We expect that a great majority of these parents are exactly who they claim to be," White said. "But we have to protect children from people who would prey on them."

Azar said the department has reassigned 230 workers to the reunification processand is completing that comprehensive case review. He said officials will soon begin sending minors to Department of Homeland Security facilities that can legally house parents and minors together. He said Homeland Security officials have already begun transferring parents to facilities closer to their children to speed up the reunification process once everybody's relationship is established.

Trump also weighed in Thursday morning, urging Congress to reform the nation's "insane" immigration laws that allow foreigners to apply for asylum or get a hearing before an immigration judge to fight deportation orders.

"When people, with or without children, enter our Country, they must be told to leave without our ... Country being forced to endure a long and costly trial," the president wrote. "Tell the people 'OUT,' and they must leave, just as they would if they were standing on your front lawn. Hiring thousands of 'judges' does not work and is not acceptable - only Country in the World that does this!"

Most developed nations have some form of refugee and asylum process. Canada, Turkey, Germany, and other nations have taken in more refugees in recent years as the global migrant crisis has mushroomed, while the U.S. has made significant cuts to its programs.