The Obama administration allowed at least 16 teenage foreigners into the United States even though it knew they were members of the so-called 'MS-13' gang, according to a Republican senator.

Senator Ron Johnson, a Republican from Wisconsin who heads the Senate Homeland Security Committee, said internal documents showed that the teenagers were sent to juvenile homes across the US, The Washington Times reported on Wednesday.

Johnson said he received the documents from a whistleblower who obtained documents from Customs and Border Protection dated 2014.

The documents include details about the 16 people who were caught crossing the border from Mexico.

'CBP apprehended them, knew they were MS-13 gang members, and they processed and disbursed them into our communities,' Johnson said.

The Obama administration allowed at least 16 teenage foreigners into the United States even though it knew they were members of the so-called 'MS-13' gang, according to a Republican senator. Suspected gang members are seen above being arrested in San Salvador in 2016

Senator Ron Johnson, a Republican from Wisconsin who heads the Senate Homeland Security Committee, said internal documents showed that the teenagers were sent to juvenile homes across the US

MS-13, or the Mara Salvatrucha, is believed by federal prosecutors to have thousands of members across the US, primarily immigrants from Central America.

It has a stronghold in Los Angeles, where it emerged in the 1980s as a neighborhood street gang.

But its true rise began after members were deported back to El Salvador in the 1990s. There, the gang thrived and spread to Honduras.

MS-13 and rival groups there now control entire towns, rape girls and young women, massacre students, bus drivers and merchants who refuse to pay extortion, and kill competitors or youths who simply refuse to join.

MS-13, or the Mara Salvatrucha, is believed by federal prosecutors to have thousands of members across the US, primarily immigrants from Central America. An MS-13 member is seen above in this 2013 file photo in El Salvador

Republicans have accused former President Barack Obama (above) of implementing lax immigration policies that allowed gang members to stream across the border into the US

That violence has prompted a migration of people trying to escape, especially children, who have streamed north because of a US policy allowing people under 18 who arrive without parents to stay in the country temporarily with relatives or friends.

Since the fall of 2013, the US has placed 165,000 unaccompanied minors.

Long Island has been a frequent landing spot. Suffolk County, which includes Brentwood and Central Islip, has gotten 4,500. Neighboring Nassau County has received 3,800.

In a recent roundup of 13 suspected MS-13 gang members accused of murder and other charges, seven had entered as unaccompanied minors.

Johnson said that a majority of unaccompanied minors who have arrived in the US are males between the ages of 15 and 17.

That, he claims, makes them prime targets for recruitment.

Johnson revealed the documents at a hearing on the dangers posed by MS-13.