Two men were arrested on Monday and a third was arrested on Tuesday, said Sweden’s Security Police, Säpo, in a statement.
The third person was being held on probable suspicion of conspiring to commit a terrorist offence. The two who were seized on Monday are suspected of attempting to commit a terrorist offence, according to Säpo.
“There’s really nothing to add,” said Jakob Larsson, press secretary at Säpo, who referred to the need for secrecy around the case.
He declined to comment on where the men were arrested, or on their nationality.
On the night of December 14th an polling station for the Iraqi election in Kista, in the north of Stockholm, was subjected to an attempted arson attack.
The attackers tried to set fire to the building with petrol bombs, but they failed to ignite. A letter which claimed to be from al-Qaida was sent to several newspapers.
The attack was clearly planned and deliberate, since the letter must have been posted before the firebombs were thrown into the building.
West Stockholm police led the investigation at first, but a few days later the case was taken over by Säpo. It is now being led by the chief prosecutor, Tomas Lindstrand.
Despite its contents, the letter is unlikely to have come from the real al-Qaida, according to the Swedish terrorism expert Magnus Ranstorp. Speaking to TT shortly after the attack, he pointed out that the logo was easy to copy and that the text seemed to be a translation from Arabic.
It tried to create the impression that an organisation was behind the attack – something which Ranstorp doubted.