(CNN) -- Swedish police arrested two individuals Saturday suspected of preparing terrorist crimes, they said.
They were responding to information that a bomb could go off in central Gothenburg, Sweden's second-largest city, on Saturday, they said.
The information was "vague and not confirmed" but police said late Friday they "could not rule out" that it was planned to explode somewhere near Nordstan, the central shopping mall.
Heavily armed police conducted a raid early Saturday morning and took a number of individuals into custody, CNN's Swedish affiliate TV4 reported.
"Overnight we managed to narrow down the investigation to a few suspects and this morning we were able to get them all," Bjor Blixter, police spokesman told TV4.
In the afternoon the prosecutor decided to formally arrest two of them on suspicion of terrorism offenses.
The others were released but are still under investigation, according to the police statement.
The Swedish Security Police, who helped local police with the investigation, could not say whether the incident was connected with Sweden raising its terror alert recently, according to TV4.
Police found out about the plot on Friday after a "credible source" contacted police, Swedish daily Aftonbladet reported.
Police increased the number of officers patrolling central Gothenburg on Saturday and the increased police presence will continue Sunday, but police did not have information to indicate that the threat would still remain on Sunday, they said.
Further arrests are likely, according to TV4.
No information was available on whether any explosives were ever found.