Stockholm - A Swedish prosecutor Monday dropped a probe over an explosives scare that caused the precautionary shut down of a nuclear reactor in May.

A so-called smear test had triggered an alert for an explosive at a spot security check on May 21. Two men, aged 53 and 44, were arrested on suspicion of planning sabotage at the Oskarshamn nuclear plant but were released the following day.

They have remained under suspicion until Monday.

Subsequent tests indicated that "a container of shaving cream" carried by one of the men contained traces of the explosive TNT or trinitrotoluene, but authorities could not explain how this occurred.

Prosecutor Gunilla Ohlin said there was "no reason to believe that a crime was committed."

A search of the plant by sniffer dogs, the men's lodgings near Oskarshamn and their homes in the town of Norrkoping did not reveal any traces of explosives and the reactor is now back on line.

Police did not find any traces of explosive on the man's hands or fingers and while there were traces of another explosive on the plastic bag used by the man, forensic analysis could not rule out contamination from a police bomb disposal vehicle used to transport the plastic bag during the alert.

Experts quoted in Swedish media at the time said the sniffing equipment was as sensitive as a dog's nose and could have triggered a false alarm.

The plant in south-eastern Sweden, operated by the energy groups E. ON of Germany and Finland's Fortum, produces about 10 per cent of Sweden's electricity. (dpa)