A man's suspicious behaviour on a bus triggered a bomb scare at Oslo central station Wednesday, partly disrupting train and bus services before it was called off, police and railway operator NSB said.
Security measures have been heightened in Oslo following last week's twin attacks that claimed 76 lives, of which eight were killed in a bomb explosion near the government's offices.
A 32-year-old Norwegian man, Anders Behring Breivik, was Monday remanded in custody on suspicion of carrying out the attacks.
The incident at Oslo central station was triggered after bus driver Jack Vadahl said he saw a male passenger jumping off his bus just as it was about to leave, apparently leaving a small suitcase behind him in the aisle.
Vadahl told reporters the man seemed "very stressed" and contacted rail operator NSB, which decided to evacuate the station and alerted police. Bomb disposal experts were deployed but did not find any explosives in the suitcase and called off the alert.
The police probe into the attacks includes investigating Breivik's claims that "two other cells" were active in Norway, and verifying his claims that he committed the attacks alone.
Efforts included tracing his international ties. Just prior to the attacks Breivik posted a 1,500-page manuscript and video on the internet, outlining his plans and views.
The far-right tract was reportedly emailed to some 1,000 email accounts. About a quarter of the names were based in Britain, the Daily Telegraph newspaper reported.
A rental car used by Breivik was an important early lead for police in establishing his identity, Oslo daily Aftenposten said.
Security camera footage of the vehicle used for the car bomb near the central government offices helped police trace the vehicle to a rental firm that provided the name of the person - Breivik - who rented the car, Aftenposten said.
Breivik used a second car from the same rental firm to drive from Oslo the island of Utoya, the scene of the shooting spree.
He was arrested Friday evening on the island in possession of two guns and a large amount of ammunition, police said.
A shooting club in Oslo has confirmed that Breivik was a member from 2005 to 2007, and again since June 2010. He attended 13 organized practice sessions but had not acted in a manner that raised suspicions about his political views, the club said in a statement.
Police late Tuesday detonated explosives at Breivik's farm about 160 kilometres north of Oslo, but did not detail what kind of explosives they were.
Late Tuesday a ceremony attended by several thousand people was held on the mainland across from Utoya island in memory of the victims, who were attending a Labour party youth camp there.