IZMIR, Türkiye

After a Swedish court on Monday ruled to keep detained four alleged Daesh/ISIS members suspected of serious weapons offenses and other charges, an expert said the Nordic country had become a "safe haven" for terrorism.

Detention hearings were held in the Nacka district court near the capital Stockholm, with two defendants, brothers, facing probable cause suspected of preparation for terrorist offences.

"All are denying crimes," judge Olof Roos told the daily Dagens Nyheter.

The four defendants were arrested by a national task force sting operation in the Tyreso municipality, south of Stockholm, last week. The operation was executed at several locations, both on Thursday and Friday.

"We have had heavy-handed leaders who used Sweden as a safe haven," Magnus Ranstorp, a political scientist and terrorism researcher, told local media on Sunday.

The four suspects allegedly belonged to a group formed by defectors from the Somali-based terrorist group al-Shabaab led by a former resident of the southwestern coastal city of Gothenburg, Abdul Qadir Mumin.

Ranstorp said Mumin lived for several years in Sweden, where he was radicalized before moving to the UK and becoming a British citizen.

The organization was founded in 2015, when Mumin and about 20 of his followers left al-Shabaab and pledged allegiance to Daesh/ISIS.