"We don't have any current active threats against the homeland, to our knowledge. And that's a good news story for today," Thomas Bossert, Assistant to the President for Homeland security and Counter-terrorism, told reporters at a White House news conference.
Earlier in the day, US President Donald Trump led the nation in mourning the death of nearly 3,000 people in the worst terror attack on the US soil 16 years ago.
Trump was given a counter-terrorism briefing on the occasion.
"The purpose of that is to give the president a sense of the terrorist threat that exists globally and to the homeland, and give him a sense of what we're doing about it, and make sure that he's comfortable with our posture," he said.