Danish police gave few details about the alleged plot during a press conference on Thursday
German authorities say they have made four arrests of suspected Hamas members linked to an alleged plot to attack Jewish sites.
Danish authorities also said they had arrested three people accused of preparing an attack.
It was not clear whether the Danish and German investigations were linked.
Danish Prime Minister Mette Frederiksen said the threat was “as serious as it gets”.
German prosecutors said in a statement that three suspects linked to Hamas were arrested in Berlin and one in the Netherlands. Hamas, which runs Gaza, is a banned terrorist group across Europe.
The three held in Berlin were Lebanese and Egyptian, according German prosecutors.
German prosecutors said the men had been charged by Hamas with retrieving weapons from a hiding place and storing them in Berlin for possible use in an attack.
Ch Insp Flemming Drejer of the Danish police said the three suspects arrested in Denmark would be charged with terror offences.
The Dutch citizen was also a suspect in the Danish inquiry, but Danish authorities have not confirmed a link with the German investigation.
The office of Israeli Prime Minister Benjamin Netanyahu wrote in a statement on X (formerly Twitter) that the seven people 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.
