A grenade exploded outside a mosque in Indonesia's restive Ambon city as worshippers gathered for prayers early on Wednesday, but there were no injuries, police said.
"It can now be ascertained that the blast was caused by a hand grenade, although we do not yet know the precise type of grenade involved," provincial police spokesman Tommy Napitupulu said.
He said morning prayers at the mosque on the island of Ambon continued despite the explosion.
The grenade attack was the latest in the past week.
An explosion at a bus station in the city injured nine people on April 25 and a few hours later, another grenade was thrown at a house.
Police are investigating whether pro-independence rebels were behind the blasts. The separatist movement was crushed shortly after its declaration in 1950 but the rebels regrouped following the fall of dictator Suharto in 1998.
Ambon was also ravaged by clashes between Muslims and Christians, which erupted in January 1999.
A peace pact in February 2002 mostly brought an end three years of strife that left more than 5,000 people dead and hundreds of thousands homeless.