"He was talking about rising crime and recent incidents in general — not referring to a specific incident," White House Deputy Press Secretary Sarah Huckabee Sanders told reporters.
But the country had spent the day baffled, because the president had said "last night" and nothing appeared to have happened.
"Sweden? Terror attack? What has he been smoking? Questions abound," Carl Bildt, a former Swedish prime minister, wrote on Twitter while he attended the Munich Security Conference on Sunday.
Sweden's Foreign Ministry spokeswoman, Catarina Axelsson, told the Associated Press that the Swedish government did not know of any "terror-linked major incidents." Additionally, the Associated Press reported, Sweden's Security Police had not seen any threats or responded to any attacks.
Sweden's U.S. embassy also appeared to take a jab at the president on Twitter Sunday evening, retweeting Trump's earlier justification and saying: "We look forward to informing the US administration about Swedish immigration and integration policies."
Trump's remarks were not the first time his administration has referred to nonexistent terror attacks while defending his executive order restricting travel for people from seven predominantly Muslim nations.
White House Counselor Kellyanne Conway invoked a "Bowling Green massacre," which never occurred. Conway has since said she made a mistake. White House Press Secretary Sean Spicer cited a nonexistent terror attack in Atlanta, then later claimed he meant the shooting at the Pulse Nightclub in Orlando, Florida — a city more than 400 miles south of Atlanta.
No terrorist attack in the U.S. has actually occurred at the hands of individuals from any of the seven countries whose people Trump's first executive order barred.
Sweden, meanwhile, has not experienced a terrorist act committed by a refugee or person of the Muslim faith since December 2010, when an Iraqi-Swedish national detonated a suicide bomb.