Danish police on Thursday arrested four people suspected of having joined the Islamic State group with the intention of committing terror.

Police spokesman Poul Kjeldsen said the four were arrested in Copenhagen and its suburbs. Arms and munitions were found in one location but it was not immediately clear whether it was connected to the arrests. Kjeldsen said he could not exclude the possibility of more arrests as the investigation continues.

Danish media showed heavily armed police outside housing complexes in Ishoej, a western suburb, and Tingbjerg, a Copenhagen neighborhood, while forensic officers walked in and out of the buildings.

Police declined to disclose further details, saying the prosecution would ask for closed doors at a pre-trial detention hearing Friday, which would bar the publication of details.

Kjeldsen said the four suspects had been identified through cooperation between Denmark's intelligence agency, known by its acronym PET, and the police in the Danish capital.

Justice Minister Soren Pind said it was too early to say what the suspects' plans were.

"We are now harvesting the fruits of our thorough efforts ... to stop foreign fighters," Pind said in a television interview.

PET's operational head, Flemming Dreyer, said people who had been in conflict zones in Syria and Iraq "could pose a terrorist threat against Denmark because of their experience and skills," but added there was no reason to change the threat assessment following Thursday's arrests.

About 60 Danish nationals have returned from Syria where they have fought alongside Islamic State members.

The case was not immediately believed to be linked to the arrest of a 20-year-old man in Sweden who has been charged with preparing to a make a suicide bomb.