Sweden heightened security at three nuclear power plants Thursday after explosives -- without triggering devices -- were found on a forklift near the country's largest power station, police said.

A truck was stopped from entering the Ringhals nuclear power plant on Wednesday afternoon and searched. The explosive paste was discovered by bomb-sniffing dogs during a security check.

The discovered object could not have induced a serious damage at Ringhals, the plant operator said in a statement reported by CNN. Ringhals nuclear power plant is still in operation.

The truck was on its way from an industrial park into a secure area. It never made it inside the facility.

There was no detonation device connected to the material. The object could not have caused serious damage at Ringhals, the company added, reported Reuters.

Investigators are looking to the incident but say the public was not in danger, even if there was a detonation device.

But even if it would have been equipped with a detonator, a potential blast would have had pretty limited effects - the truck would have received some damage and perhaps some passers-by would have been injured, but it wouldn't have harmed the plant in any way, police spokesman Tommy Nyman said, the Associated Press reported.

Nyman mainted the exploves would not have been able to disrupt power generation at the plant.

Immediately after the incident, the plant raised its security levels from its lowest levels to a 4 as a precaution. Officers began patrolling nuclear power sites overnight with bomb-sniffing dogs. They found no other threat.

The country's other power plants in Forsmark and Oksarshamn also increased their security measures.

It is still assessed that there was no risk of an explosion because the explosive had no detonation device, the statement continued, according to CNN.

Police said the driver of the truck was unaware the explovies were in his vehicle. They not consider him a suspect. Authorities are still looking for leads, motives and people of interest in the case.

An outsider has obviously placed them on the truck, Nyman said, reported the AP. We're talking to the truck driver and are trying to map out her movements within the (Ringhals) premises throughout the day.

Martina Kruger, head of the Climate and Energy Division at Greenpeace in the Nordic region, criticized the police and Swedish government for downplaying the incident.

It doesn't matter if it was outside the protected area or not, it shouldn't have made itself within the premises at all, she said, reported the AP.

While police search for the people responsible, Magnus Norell of the Swedish Defense Research Agency said they must remain vigilant of other potential threats. He said someone might have been testing the response and readiness of the Swedish police.

It could suggest that someone was testing it to do something serious later on. But it's all pure speculation right now as we have so little information, he said. It shows the system did work. They picked up on it and nothing happened. That's one good signal.