Banda Aceh, Indonesia – A grenade exploded outside the office of former separatist rebels in Indonesia's once-restive Aceh province Thursday, but no one was reported injured, a police official said.

Resource-rich Aceh was torn by conflict for nearly 30 years before a peace deal between Jakarta and the separatist Free Aceh Movement (GAM) in 2005.

The peace agreement has generally been regarded as successful although there are concerns next year's election could fan tensions in the province on the northern tip of Sumatra.

The blast damaged two cars and the office windows of the Aceh Transitional Commission (KPA) office, said Ilsarudin, police chief of the provincial capital, Banda Aceh. Police were questioning four witnesses, he added.

The explosion occurred about two weeks after the GAM founder, Hasan di Tiro, returned home from Sweden after more than 30 years in exile. (Writing by Telly Nathalia; Editing by Sugita Katyal and Bill Tarrant)