Two men arrested after an explosives scare at a Swedish nuclear plant were released Thursday and police said they were no longer considered a threat to the power station.

The two maintenance workers were arrested Wednesday after security guards at the Oskarshamn nuclear plant found traces of a highly explosive substance on a plastic bag that one of them was carrying.

The incident triggered a major security alert, prompting officials to shut down one of the plant's three reactors as bomb squads searched for explosives. None were found.

After keeping the two middle-aged Swedes in custody overnight, investigators said there was not enough evidence to keep them in jail on suspicion of plotting sabotage.

"There was no reason to keep them under arrest anymore, but the suspicions against them remain," Prosecutor Gunilla Ohlin told The Associated Press.

She said investigators were awaiting the results of an analysis of the substance, believed to be to be triacetone triperoxide, or TATP, an explosive that was used in the 2005 London transit bombings.

Police did not release the suspects' identities, saying only that one was born in 1955 and the other in 1962 and both were Swedish citizens from the city of Norrkoping.

Police spokesman Sven-Erik Karlsson said they were no longer considered a threat to the nuclear plant, but declined to elaborate. He added it was still unclear how traces of the explosive ended up on the handle of the plastic bag being carried by one of the men.

"He can't explain it and no other explanations have emerged either," Karlsson said.

TATP is made by mixing chemicals used in common household items, including hydrogen peroxide and paint thinner. Continued...