Security has been ramped up at Sweden's nuclear power plants after bomb-sniffing dogs detected explosives in a truck at the southwestern Ringhals atomic power station.

Officials are not revealing the type of explosives found but have said that the material lacked a detonation device to set them off. The vehicle was at a routine checkpoint outside the high security enclosure when the explosives were discovered. Officals, without saying how they arrived at their assesment, say that the explosives wouldn’t have caused any serious damage to the facility.

The driver of the truck said that she has no idea how the explosives came to be in his truck. Officials believe that she is telling the truth and she is not considered a suspect.

“An outsider has obviously placed them on the truck,” Police spokesman Tommy Nyman said. “We’re talking to the truck driver and are trying to map out her movements within the (Ringhals) premises throughout the day.”

The country’s four-stage Security Alert scale has been raised to two.

Voters in Sweden voted to phase out nuclear power plants in 1980, but two years ago, that decision was reversed because of the lack of viable long term environmentally friendly alternatives.