BANDA ACEH, Indonesia, Sept 17 (Reuters) - The office of a political party made up mainly of former separatist rebels in Indonesia's Aceh province was attacked by a grenade on Wednesday, causing damage but no casualties, officials 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 elections could fan tensions in the province on the tip of Sumatra.

The attack damaged office equipment in the Bireun branch of the Aceh Party, one of six parties in the province eligible to contest parliamentary and provincial elections next year, said party spokesman Ibrahim.

A local police officer said the blast was being investigated. (Writing by Telly Nathalia; Editing by Ed Davies and Jerry Norton)

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