Johnson, FBI Director James Comey and National Counterterrorism Center Director Nicholas Rasmussen all were pressed on a range of security issues by the Homeland Security Committee, including migration, cyber hackers manipulating voting systems and recent bombings in New York City and New Jersey.
Johnson told the committee his agency has established a working group in recent months to crack down on smuggling groups bringing Middle Eastern migrants across the southern US border. He said the new group works with the law enforcement in Central and South America to "interdict these people before they get to our border and share intelligence about what we're seeing."
Johnson said the group is focused on the smuggling networks that are moving Middle Eastern migrants, whose numbers have risen in the past year.
Asked about cyber security threats, Johnson told the committee that 18 US states have accepted his agency's offer to help secure their voting systems from hackers ahead of the Nov. 8 election.
In August, the Federal Bureau of Investigation said voter databases in two states had been breached.
Johnson also was pressed about immigrants mistakenly granted citizenship, as revealed last week in a Department of Homeland Security Inspector General report.
Johnson said his agency was reviewing the cases and revoking citizenship for cases in which it was wrongly granted.
Comey said the investigation into Ahamad Rahami, the suspect behind the recent bombings in New York City and New Jersey, so far does not point to a wider terror cell or future attacks.
Department of Homeland Security Secretary Jeh Johnson testifies at the Senate Homeland Security and Governmental Affairs Committee in Washington, US.
US Department of Homeland Security Secretary Jeh Johnson told a Senate panel on Tuesday the United States was cracking down on Middle Eastern migrants illegally crossing the southern US border.
