Homeland Security Secretary Kirstjen Nielsen claimed Monday that the crisis of illegal immigrant children being housed separately from the adults who bring them across the border is, in part, fueled by men and women making fake asylum claims with children who aren't theirs.

'From October 2017 to this February, we have seen a staggering 315 per cent increase in illegal aliens fraudulently using children to pose as family units to gain entry into the country,' she told the annual National Association of Sheriffs meeting in New Orleans.

'This must stop. All this does is put the children at risk.'

White House spokeswoman Mercedes Schlapp added in a Fox News Channel interview that one example of a fraudster is 'an MS-13 gang member walking in with a one-year-old.'

A Department of Homeland Security official told DailyMail.com on Monday that the 315 per cent increase refers to a comparison between 46 such cases during the government's fiscal year 2017, and 191 cases during just the first five months of fiscal 2018, which ran from September 2017 to February 2018.

Despite the low raw numbers, extrapolating that more recent total to a 12-month period would produce a tenfold increase from 2017 to 2018.

The DHS official said the Obama administration never tracked those numbers, so Trump administration agency workers had to comb through the cases and hand-count those where entering children were determined not to be related to the adults they traveled with.

Homeland Security Secretary Kirstjen Nielsen claimed Monday that asylum-claiming fraudsters are bringing children who aren't theirs across the U.S. Mexico border, often resulting in the minors being held in detention alone

Are they related? Nielsen said there has been a 315 per cent increase in people falsely claiming to be 'family units' when they arrive and claim asylum after sneaking across the border

White House spokeswoman Mercedes Schlapp (right) said one example of an asylum fraudster is 'an MS-13 gang member walking in with a one-year-old'

Nielsen said Monday that 'we do not have the luxury of pretending that all individuals coming to this country as a family unit are in fact a family,' Nielsen added. 'We have to do our job. We will not apologize for doing our job.'

And, she said, DHS is asking Congress 'to allow us to keep families together while they are detained.'

Democratic lawmakers and immigration advocates pilloried The Trump administration all weekend with complaints about 'evil' and 'un-American' treatment of children who are brought across the U.S.-Mexico border and then separated from their parents.

In past administrations, entering the country as a family unit was one way to guarantee illegal immigrants a favorable outcome since court decisions have rendered the Department of Health and Human Services unable to hold children in shelters for more than 20 days.

The result was typically the release of children with the adults into the interior of the United States to await court hearings. Large numbers ultimately were no-shows.

'We've seen the release of over 200,000 family units into the United States since 2016,' Schlapp said. 'I mean, that's incredibly problematic.'

'You've had these smugglers who've been able to basically perfect the business model when it comes to bringing these children over,' she added.

Nielsen said Monday that the children have often represented a well-publicized 'get-out-of-jail-free-card' that the Trump administration stopped handing out with the adoption of a zero-tolerance policy two months ago.

She also said America's low bar for establishing asylum-seekers' 'credible fear' of persecution or physical harm in their home countries.

Nielsen reminded foreign nationals that asylum seekers can make their claims at regular ports of entry and don't need to come in illegally

Secretary Nielsen drew fire for insisting on Sunday that the media and members of Congress are 'misreporting' details of the border crisis and how it's impacted by federal law

'As a result, over the last seven years we've seen the number of individuals claiming asylum skyrocket,' she said.

And 'we've asked Congress to adjust the standard of proof to prevent well-coached applicants from uttering the magic words indicating a fear of returning home.'

Justice Department figures show that 80 per cent of asylum claims are ultimately rejected, but initial false claims stretch out the adjudication process.

Speaking to people with legitimate claims, Nielsen said: 'You do not need to break the law of this country by entering illegally to claim asylum. If you are seeking asylum go to a port of entry.'

Adding to the high-profile crisis at the border are other federal laws that treat Mexican nationals differently from people of other nations.

Mexicans can be returned quickly and directly to Mexico. But Guatemalans and Salvadorans, for example, cannot.

A quirk in federal law allows DHS to deport Mexicans quickly and directly back to Mexico, but Hondurans like this woman and child can't be sent back until a long administrative process has been completed

Border agents have reportedly been telling illegal immigrant parents that they are taking their children 'for a bath' before separating them. This heartbreaking photo shows the children at a Border Patrol processing facility in McAllen, Texas

Anne Chandler, the director of the Houston office of Tahirih Justice Center said she's spoken with several parents who said they were told their children were going to get a bath before they were separated

Children who originate from south of Mexico and travel the length of that country before arriving in the U.S., Nielsen said, must by law be handed over to HHS within 72 hours.

'Why is our system built on treating people from Mexico and Canada different than any other country?' she asked.

Nielsen attacked reporters and members of Congress on Sunday for 'misreporting' details of the administration's immigration policy.

She said 'advocacy groups' were unfairly blaming the president and her agency for a policy that results in separating nearly 2,000 children from their parents.

'We do not have a policy of separating families at the border. Period,' she tweeted, drawing howls of protest from journalists and Democratic partisans.

Nielsen called the president's opponents 'irresponsible and unproductive' for turning the border situation into an international story.

'As I have said many times before, if you are seeking asylum for your family, there is no reason to break the law and illegally cross between ports of entry,' she tweeted.

She explained: 'For those seeking asylum at ports of entry, we have continued the policy from previous Administrations and will only separate [families] if the child is in danger, there is no custodial relationship between "family" members, or if the adult has broken a law.'