JAKARTA, March 2 (Reuters) - A 100-strong mob set fire to the the offices of former separatist rebels in Indonesia's Aceh province, killing four people and throwing another down a well, the head of local police said on Sunday.

The crowd attacked the buildings of the Aceh Transitional Commission in the remote Atu Lintang area in the centre of the province midnight on Friday, AB Kawendar told Reuters by telephone.

"We are still investigating the motive behind the attack," said Kawendar, who said that four people died in the blaze and one was thrown into a 35 metre (115 ft) well.

Another person was seriously wounded and was being treated in hospital.

Resource-rich Aceh was torn by conflict for nearly 30 years before the December 2004 tsunami devastation spurred a peace agreement between Jakarta and the separatist Free Aceh Movement (GAM).

A former GAM rebel, Irwandi Yusuf, took over as the governor of the province last year further cementing the peace deal, but there have been sporadic incidents of violence since, often over the sharing of resources in the province.

Seven police officers on the site could not stop the attack and it took several hours for back-up to arrive, the police official said. There had been no arrests so far.

(Reporting by Ade Mardiyati, Writing by Ed Davies; Editing by Sanjeev Miglani)

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