Danish police gave few details about the alleged plot during a press conference on Thursday
German and Danish authorities say they have made arrests in connection with alleged plans to stage attacks on Jewish sites.
Three people in Germany, three in Denmark and one in the Netherlands were arrested on Thursday, according to authorities.
Danish Prime Minister Mette Frederiksen said the threat was “as serious as it gets”.
German prosecutors said four were suspected Hamas members.
Three of the suspects were arrested in Berlin and one in the Netherlands, they said in a statement. Hamas, which runs Gaza, is a banned terrorist group across Europe.
The suspects had planned to attack Jewish sites in Europe, prosecutors said.
A 57-year-old Dutch citizen was arrested in Rotterdam as part of the German investigation.
Dutch reports said he was also a suspect in the Danish inquiry, but Danish authorities have not confirmed a link with the German investigation.
The three held in Berlin were Lebanese and Egyptian, according German prosecutors.
The three suspects arrested in Denmark would be charged with terror offences, Ch Insp Flemming Drejer told reporters.
The office of Israeli Prime Minister Benjamin Netanyahu wrote in a statement on X (formerly Twitter) that those arrested were “acting on behalf of Hamas”. While federal prosecutors in Germany linked the plot to Hamas, Danish authorities have not confirmed any links to the group.
Danish Justice Minister Peter Hummelgaard said the alleged plot “tragically confirms that Danish Jews are under threat”.
Those arrested in Denmark were scheduled to appear in closed court hearings on Thursday.
Ch Insp Drejer said an investigation had uncovered a transnational network of people preparing an attack, with links to criminal gangs.
Security around Jewish sites would be reinforced and police patrols in Copenhagen made more frequent, he added.
Danish intelligence chief Anja Dalgaard-Nielsen said the terror threat was linked to the Israel-Gaza war and burnings of the Quran in Denmark and neighbouring Sweden.
The terror threat in Denmark currently stands at level four out of five, the second-highest. The PET security and intelligence agency says the main threat to Denmark comes from militant Islamists, most likely from” a small group or a lone actor” inspired by propaganda.
Mr Hummelgaard said the government currently saw no reason to raise the threat level.