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Norwegian police said on Wednesday they were searching for a man suspected of threatening to blow up parliament and cordoned the building off.
A man who was apprehended overnight when police raided an apartment building in south-east Oslo was released after questioning and ruled out of the probe, police said.
They were investigating other leads, they said.
A passenger on a regional bus bound for Oslo late on Tuesday alerted police after hearing a man making threats on the bus to other passengers.
The suspect then got off and was seen taking a taxi from Sandvika, west of Oslo, and was reported to be carrying a heavy bag and a bullet-proof vest.
In July 2011, convicted right-wing terrorist Anders Behring Breivik set off a car bomb outside the government headquarters which killed eight people and damaged nearby buildings. - Sapa-dpa