Thieves have stolen 660kg (1400lb) of dynamite from an unstaffed storage depot in Norway, say police.
The theft raised fears of Madrid-style attacks in Norway
Around 5,000 detonators were also stolen, raising fears of a terrorist attack, officials told state radio.
The missing dynamite was more than six times the amount used for the bomb attacks on trains in Madrid nearly a month ago.
Last May, a taped message attributed to al-Qaeda's second-in-command urged Muslim militants to hit Norway.
In the message, a man identified as al-Qaeda deputy leader Ayman al-Zawahri advocated attacks on the embassies and interests of the United States, Britain, Australia and Norway, to drive them from Muslim countries.
The NRK state radio network reported that the storage depot, on the outskirts of the remote town of Gol, had a fence and heavy doors - but no alarm system.
Explosives depots in Norway are generally built far from populated areas, for safety reasons.
Police could not identify any suspects or motive for the theft, nor could they establish when it happened.
The theft was discovered Wednesday - six days after the depot was last inspected.
Odd Ropstadt, from the Civil Protection and Emergency Planning agency, said 660kg of dynamite was "more than enough to create all the terror someone might desire".
"Explosives are something that terrorists will always be looking for," he said.
"In Norway, we have been very naive when it comes to explosives.
"We have to prepare for a different future."