An Immigration and Customs Enforcement pilot of new rapid DNA testing at the border has found that nearly a third of those tested were not biologically related to the children in their custody.

ICE conducted the pilot for a few days earlier this month in El Paso and McAllen, Texas, finding about 30 per cent of those tested were not related to the children they claimed were their own, an official told the Washington Examiner.

The official said that these were not cases of step-fathers or adoptive parents.

'Those were not the case. In these cases, they are misrepresented as family members,' the official said.

Border Patrol agents are seen processing a family unit in Texas earlier this month. A pilot program of DNA testing found that 30 per cent of those tested had lied about family ties

Central Americans who cross the border illegally with children can claim asylum and avoid any lengthy detention in most cases. Migrants are seen in March after illegally entering Texas

It is unclear whether every family unit was tested during the pilot, or only those who raised some sort of red flag. An ICE spokesman did not immediately respond to request for comment.

The official said that some migrants did refuse the test and admit that they were not related to the children they were with, when they learned their claim would be subjected to DNA proof.

ICE said the Department of Homeland Security would look at the results of the pilot to determine whether to roll out rapid DNA tests more broadly.

After President Donald Trump's administration backpedaled on 'family separation' in the face of enormous backlash last summer, the number of family units arriving at the southern border has skyrocketed.

Current U.S. law and policy means that Central Americans who cross the border illegally with children can claim asylum and avoid any lengthy detention in most cases.

Migrants are seen outside the U.S. Border Patrol McAllen Station in a makeshift encampment in McAllen, Texas earlier this month

U.S. Border Patrol McAllen Station has been inundated with migrant family units

US Border Patrol says it has apprehended 535,000 for crossing the border illegally so far this year, with 'no sign of it getting better.'

Due to massive strain on the processing system, 40,000 of those have been released into communities, the agency said.

On Saturday, the Trump administration told lawmakers that it probably will cost more to care for migrants crossing into the United States from Mexico than the $2.9 billion in emergency money requested just two weeks ago.

In a White House letter, acting budget chief Russell Vought said 'the situation has continued to deteriorate and is exceeding previous high end estimates.'

Health and Human Services Secretary Alex Azar said in a separate letter that needs for the unaccompanied children account 'could grow further and be closer to the worst-case scenario HHS had proposed be the basis for the supplemental request, which was $1.4 billion higher.'