Story highlights The MS-13 gang began in the US and was exported to Central America

It has been impossible to assess the impact of illegal immigration on the group

Washington (CNN) President Donald Trump on Thursday made a sweeping assertion that the MS-13 gang has "literally taken over" US cities -- but his remarks about the violent street gang contained a number of misstatements or claims that were impossible to back up with evidence.

MS-13 has been a frequent talking point of the Trump administration as part of its justification for hard-line immigration policies and border security. It was in that context that Trump brought up MS-13 in his opening statement in a joint news conference with Colombian President Juan Manuel Santos -- as he talked about stopping trans-border crime.

"MS-13, likewise, a horrible, horrible large group of gangs that have been let into country over a fairly short period of time are being decimated by the Border Patrol and by ICE and by our incredible local police forces and they are getting out of our country or in some cases, going directly into prisons throughout our country," Trump said. "But they've literally taken over towns and cities of the United States."

Trump's comments contained a number of mischaracterizations of MS-13 or assertions that are not backed up by any statistics.

While Colombia is an important front in the fight against gangs and drugs, MS-13 is a Central American and US-based gang, so Trump's mention of the issue seemed unrelated to his conversation with Santos.

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