WASHINGTON (Reuters) - Over 1,500 immigrant children who have entered the United States unaccompanied are not “lost,” as Senate testimony by an administration official in April suggested, a U.S. Health and Human Services official said on Monday, as outrage over their treatment triggered a social media storm.

FILE PHOTO: U.S. acting Secretary of Health and Human Services (HHS) Eric Hargan addresses reporters during the daily news briefing at the White House in Washington, U.S., November 30, 2017. REUTERS/Jonathan Ernst/File Photo

Deputy HHS Secretary Eric Hargan issued a statement and fact sheet on Monday night saying the department’s Office of Refugee Resettlement attempted to follow up on the 2016 release of unaccompanied children by contacting their families, a step he said was not required of the department.

Following recent news reports of children lost in the system after crossing the border illegally, outrage erupted on social media in recent days after reports emerged that HHS over the past three months of 2017 lost track of 1,475 children who crossed into the United States from Mexico by themselves and were placed with sponsors.

The figures had been cited by HHS official Steven Wagner in Senate hearing testimony in late April.

“These children are not ‘lost’; their sponsors—who are usually parents or family members and in all cases have been vetted for criminality and ability to provide for them—simply did not respond or could not be reached when this voluntary call was made,” Hargan said in a statement.

Hargan said that despite voluntary efforts by HHS to check up on their whereabouts, sponsors often did not answer their calls because they themselves were illegal immigrants, which he said revealed a ” fundamental flaw” in U.S. immigration policy that incentivized immigrants to break immigration laws.

President Donald Trump and high-level administration officials have been defending the policy of separating immigrant children from their parents as part of tougher border enforcement measures initiated in recent weeks.

Lawyers representing immigrants have called the administration’s policies separating children from their parents cruel and inhumane.

In a Twitter message on Saturday, Trump blamed Democrats for the current law that enables children to be separated from their parents once they cross the border.

In the fact sheet released on Monday, Hargan said loopholes in immigration law had driven the surge in separations of unaccompanied children and their families.

The fact sheet cites Wagner, who says the unaccompanied alien children program “is being abused” at the expense of taxpayers.

“It was never intended to be a foster care system with more than 10,000 children in custody at an immediate cost to the federal taxpayer of over one billion dollars per year,” the fact sheet said.

The fact sheet also said the only solution to the problem was to “change federal law so that illegal immigrants can be returned after they are apprehended.”