WASHINGTON — In an interview Sunday morning on ABC's "This Week," Homeland Security Secretary Alejandro Mayorkas warned of a "very difficult threat landscape" in the wake of the New Orleans truck attack.

"We have not only the persistent threat of foreign terrorism -- that, of course, created the Department of Homeland Security -- but we have adverse nation-states, and for the past 10 years, we've seen a significant increase in what we term 'homegrown violent extremism,'" Mayorkas told anchor George Stephanopoulos. "It is a very difficult threat landscape, and it is why that we as a community -- not just the federal government, but state and local officials and residents -- need to be alert to it and take the precautions necessary to avoid violence from occurring."

Mayorkas emphasized that, despite immigration being the department's "highest responsibility," the New Orleans attack was unrelated to issues at the border.

"The assailant who perpetrated the terrorist attack in New Orleans was born in the United States, raised in the United States, and served in our armed forces," he said. "It is not an issue of the border."

Mayorkas said he has been in touch with South Dakota Gov. Kristi Noem, President-elect Donald Trump's pick for secretary of the Department of Homeland Security.

“I have spoken with Governor Noem a number of times, including on New Year's Day and immediately thereafter, with respect to the horrific terrorist attack, and we have spoken substantively about the measures that we take, and I am incredibly devoted to a smooth and successful transition to the success of Governor Noem should she be confirmed as the Secretary of Homeland Security," he said.

Republican Rep. Michael McCaul, who appeared on "This Week" after Mayorkas, warned of a resurgence of ISIS activity that he said "concerns me greatly."

McCaul advised the Trump administration to be wary of attacks by those who become radicalized online, urging officials to "pay attention to the social media and connect the dots before these events happen."

"You really have two types of threats. One is operational, the other one is inspired attacks radicalized over the internet," McCaul said. "They're both equally lethal, and they need to be focused on to stop it."

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