On Wednesday morning a handyman was stopped at the entrance to the nuclear power plant in Oskarshamn because a scanner detected traces of explosives in his bag, German newspaper Handelsblatt said in its Thursday edition. It wasn't a bomb, however, but traces of the highly explosive chemical substance TATP. The man said he didn't know how the substance got there, and was later released.

In the afternoon two men ages 53 and 44 were arrested because they are suspected of planning to sabotage the power plant. The men were working in Oskarshamn's reactor No. 2, which was taken offline in May for maintenance work, Handelsblatt said.

Police later Wednesday searched the reactor with dogs and technical equipment, and reactor No. 1 was also shut down as a precautionary security measure, officials said.

The Oskarshamn plant is run by OKG, with the main shareholder being German energy giant E.ON. The incident comes almost two years after two emergency generators of the Swedish Forsmark 1 reactor, roughly 120 miles north of Stockholm, malfunctioned during a power failure. Forsmark is also owned by E.ON.