STOCKHOLM/WEST PALM BEACH, Fla. (Reuters) - A day after falsely suggesting there was an immigration-related security incident in Sweden, President Donald Trump said on Sunday his comment was based on a television report he had seen.

Trump, who in his first weeks in office has tried to tighten U.S. borders sharply for national security reasons, told thousands of supporters at a rally on Saturday that Sweden was having serious problems with immigrants.

"You look at what's happening last night in Sweden," Trump said. "Sweden. Who would believe this? Sweden. They took in large numbers. They're having problems like they never thought possible."

No incident occurred in Sweden and the country's baffled government asked the U.S. State Department to explain what Trump meant.

"My statement as to what's happening in Sweden was in reference to a story that was broadcast on @FoxNews concerning immigrants & Sweden," Trump said in a tweet on Sunday.

My statement as to what's happening in Sweden was in reference to a story that was broadcast on @FoxNews concerning immigrants & Sweden. — Donald J. Trump (@realDonaldTrump) February 19, 2017

Fox News, a U.S. cable news channel that has sometimes been cited favorably by Trump, ran a report on Friday night about alleged migrant-related crime problems in the country.

A White House spokeswoman told reporters on Sunday that Trump had been referring generally to rising crime and not a specific incident in the Scandinavian country.

Sweden's crime rate has fallen since 2005, official statistics show, even as the country has taken in hundreds of thousands of immigrants from war-torn countries like Syria and Iraq.

Trump's comment confounded Sweden's government. "We are trying to get clarity," Foreign Ministry spokeswoman Catarina Axelsson said.

The U.S. State Department said it did not comment on diplomatic communications.

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Trump has been widely criticized for making assertions with little supporting evidence.

In recent months, he has argued that more than 3 million people voted fraudulently in the U.S. election, an assertion that election officials say is false, and incorrectly stated that he won the election by the most decisive margin in decades.

Swedish Foreign Minister Margot Wallstrom appeared to respond to Trump's statement about her country on Saturday by posting on Twitter an excerpt of a recent speech in which she said democracy and diplomacy "require us to respect science, facts and the media."

Her predecessor was less circumspect.

"Sweden? Terror attack? What has he been smoking? Questions abound," former Swedish Foreign Minister Carl Bildt wrote on Twitter.

Other Swedes mocked Trump's remark on Twitter using the hashtag #LastNightInSweden, posting pictures of reindeer, Swedish meatballs and people assembling the country's famous IKEA furniture.

"#lastnightinsweden my son dropped his hotdog in the campfire. So sad!" Twitter user Adam Bergsveen wrote.

(Reporting by Anna Ringstrom in Stockholm, Andy Sullivan in Washington and Jeff Mason in Florida; Editing by Kieran Murray and Peter Cooney)