The Department of Homeland Security definitively debunked the persistent right-wing media conspiracy theory that Islamic State fighters have attempted to cross the U.S.-Mexico border, saying the rumor is not supported by any “credible intelligence” and knocking the claim that the terrorists have been apprehended at the border as “categorically false.” 

What began early this summer as an unsubstantiated claim from Texas Gov. Rick Perry (R) that “people that are coming [across the U.S.-Mexico border] from states like Syria that have substantial connections back to terrorist regimes and terrorist operations,” (a claim PolitiFact Texas rated “Pants on Fire”), has morphed into a full-blown right-wing conspiracy theory. Conservative media and elected officials are hyping fears that members of the Islamic State (ISIS or ISIL) terrorist group are utilizing the U.S.-Mexico border to enter the U.S. and launch terrorist attacks, a chorus that has only grown louder in the ensuing months to attack immigration reform.

In September, Rep. Jason Chaffetz (R-UT) claimed to have seen information detailing “four individuals trying to cross through the Texas border who were apprehended at two different stations that do have ties to known terrorists organizations in the Middle East,” a story subsequently hyped by Fox News. Nearly a month later, the number had jumped from four terrorists allegedly apprehended to 10.

Fox News' On The Record provided a platform to Rep. Duncan Hunter (R-CA) who claimed to have first-hand knowledge of the terrorists crossing the border. Host Greta Van Susteren replied to Hunter's allegations by asking, “Do you have any information, or any evidence, that they are actually coming in the southern border now?” And Hunter responded, “Yes. ... I know that at least 10 ISIS fighters have been caught coming across the Mexican border in Texas,” citing information he'd received from border patrol agents.

But the right-wing talking point is “categorically false,” according to the Department of Homeland Security, which oversees border security. On October 8, DHS spokesperson Marsha Catron refuted the rumor that Islamic State terrorists had crossed the U.S.-Mexico border, telling The New Republic: 

“The suggestion that individuals who have ties to ISIL have been apprehended at the Southwest border is categorically false, and not supported by any credible intelligence or the facts on the ground,” said DHS spokesperson Marsha Catron. “DHS continues to have no credible intelligence to suggest terrorist organizations are actively plotting to cross the southwest border.”

It remains to be seen whether DHS's facts permeate the right-wing bubble. After hearing the DHS statement, Sean Hannity claimed on his radio program that the agency could not be trusted and suggested it may be lying.

UPDATE: In remarks to the Center for Strategic & International Studies Statesmen's Forum on October 9, DHS Secretary Jeh Johnson explained that four men were apprehended at the southern border in September and investigated for ties to terrorist organizations. 

The Department found that the men were self-declared members of the Kurdish Worker's Party, a group which has defended Kurdish territory in Iraq against incursions from the Islamic State. Johnson said that the men had been arrested for unlawful entry, detained, and would be deported.

Media Matters researcher Jess Torres contributed research to this post.