COPENHAGEN, Denmark (AP) - Swedish officials say three people have been arrested on suspicion of preparing "an act of terror."

Sweden's domestic intelligence agency SAPO says the three were arrested Monday for terror-related activities in several locations in greater Stockholm. SAPO said they had been on the agency's radar for a while.

The agency says several other people have been brought in for questioning.

It added that the terror threat in Sweden remains "unchanged" at a rating of three on a five-degree scale, which is "an increased threat."

In April 2017, an Uzbek man rammed a stolen truck into a shopping crowd in Stockholm, killing five people and injuring 14 others. He said he did it to punish Sweden for joining a coalition against the Islamic State group in the Mideast.

Copyright 2018 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.