Danish prime minister Mette Frederiksen was assaulted by a man in the capital Copenhagen, the state news agency Ritzau has reported.
Copenhagen police confirmed on the X social media platform that one person was arrested in the case and an investigation was under way.
There was no immediate word on how the assault happened or if Ms Frederiksen was hurt in any way.
The prime minister’s office told the Danish state broadcaster DR that she was “shocked” by the incident.
The reports gave no further details and it was unclear in what context the assault happened, but it came just ahead of the European Union parliamentary elections on Sunday.
Ms Frederiksen has been campaigning with the Social Democrats’ EU lead candidate, Christel Schaldemose.
Media reports said the attack was not linked to a campaign event.
News of the assault was received with shock and condemnation by politicians across the political spectrum inside the Scandinavian country and abroad.
Swedish Prime Minister Ulf Kristersson said that “an attack on a democratically elected leader is also an attack on our democracy”, while Charles Michel, president of the European Council, condemned on X what he called a “cowardly act of aggression”.
Violence against politicians has become a theme in the run-up to the EU elections. In May, a candidate from Germany’s centre-left Social Democrats was beaten and seriously injured while campaigning for a seat in the European Parliament.
In Slovakia, the election campaign was overshadowed by an attempt to assassinate populist prime minister Robert Fico on May 15, sending shockwaves through the nation of 5.4 million and reverberating throughout Europe.
