Three people have been arrested on suspicion of preparing "an act of terror" in Sweden.

Sweden's domestic intelligence agency SAPO says the three were arrested today for terror-related activities in several locations in greater Stockholm.

SAPO said the trio had been on the agency's radar for a while, with several other people also 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, illing 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.

- Press Association and Digital Desk