About 20 people have been arrested on suspicion of involvement in Islamist terrorism after a series of raids across Denmark, authorities have said.

Flemming Drejer, the operative head of the Denmark’s Security and Intelligence Service, said the detainees were suspected to have been “driven by a militant, Islamist motive”. Copenhagen police’s chief inspector, Jørgen Bergen Skov, said some of them would be charged behind closed doors on Thursday under the country’s terrorism laws.

“Some have procured things to make explosives and have tried to acquire weapons,” Bergen Skov told a joint press conference with the domestic intelligence service.

Bergen Skov said six police departments across the country raided about 20 properties. The raids and arrests were coordinated by Copenhagen police.

No details were given as to what the alleged terrorists’ target was believed to be nor when an attack might have taken place.

Danish authorities have reported foiling several extremist attacks in recent years, including plots linked to the publication in a newspaper in 2005 of 12 cartoons by various artists depicting the prophet Muhammad.

A Danish court this year gave a Syrian asylum seeker in Sweden a 12-year prison sentence for planning to plant one or more bombs in Copenhagen and stab random people with kitchen knives. Moyed al-Zoebi, 32, acted on behalf of Islamic State, according to the Copenhagen city court.

An accomplice, Dieab Khadigah, was sentenced in Germany in July 2017 to a prison term of six and a half years.