A Swedish district court has ordered three men with reported terrorist ties detained on suspicion of plotting a murder.

Authorities in the western city of Gothenburg arrested the three men initially on suspicion of plotting a terror attack. A fourth person also was arrested, but was later released for lack of evidence. They were arrested in a sting operation on Sunday, the 10th anniversary of the September 11 attacks in the United States.

There were unconfirmed reports the men were connected to the al-Qaida-linked Somali militia, al-Shabab. But the prosecutor in the case said the terror charges were dropped in part because it could not be proven that the alleged crimes posed a threat against the Swedish state. The prosecutor also refused to name the target of the alleged murder plot during the ongoing investigation.

However, in connection with the arrests, police evacuated several hundred people from an exhibition hall where an art show was set to make its debut.