Islamic State extremists have discussed infiltrating the U.S. through its southern border with Mexico, a U.S. official said.

Francis Taylor, undersecretary for intelligence and analysis at the Department of Homeland Security, told a Senate committee Wednesday that the Sunni militants have been tracked discussing the idea on social media sites such as Twitter Inc.

¡°There have been Twitter and social media exchanges among ISIL adherents across the globe speaking about that as a possibility,¡± Taylor said. Islamic State is also known by the acronyms ISIL and ISIS. Referring to the 1,933-mile (3,110- km) boundary with Mexico, Taylor said he was ¡°satisfied that we have the intelligence and the capability at our border that would prevent that activity.¡±