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MERCER ISLAND, Wash. (JTA) — An explosive device went off last week outside the Stroum Jewish Community Center here, according to local police.

It blew up in the parking lot Monday evening, when many parents were picking up their children from after-school programs at the JCC in this Seattle suburb.

No injuries or property damage were reported.

"It was definitely an explosive device that was set off intentionally at that location," said Sgt. Alan Lacy. "The JCC staff has received no telephone calls or letters from anybody claiming responsibility for it."

Lacy said police collected fragments of the explosive device, believed to be "about the size of a large firework."

The preliminary police report noted that fragments, including part of a kitchen timer, timing mechanism, battery pack and metal pipe end-cap, were recovered at the site of the explosion. There was no damage to the parking lot or cars parked nearby, the report said.

"There's no way of knowing if this was an anti-Semitic incident," said Marvin Stern, regional director of the Anti-Defamation League.

The ADL distributed a letter to area Jewish agencies, suggesting that they be "especially cautious and aware of any unusual activity" taking place at their facilities, paying special attention to mail delivery and unfamiliar visitors.

Stern said the ADL would "prefer to err on the side of prudence in raising people's awareness that this incident took place, and may in fact have been an anti-Semitic incident."

Police have increased the number of patrol officers to the area.