By Lucy Williamson
BBC News, Aceh
Indonesia's military says its mission is to ensure security in Aceh
Hostility between the Indonesian army and former rebels in the province of Aceh is at its highest point since the peace deal in 2005.
This is the conclusion of a new report by the International Crisis Group.
It says tensions are high ahead of elections next month, though it is unlikely the violence will escalate again into full-blown conflict.
Following the 2004 Asian tsunami, a peace deal put an end to 30 years of civil war.
The deal was between the Indonesian government and independence fighters from the Free Aceh Movement (GAM).
'Fear and loathing'
The crux of the problem is what the report calls "fear and loathing" between the former GAM rebels and the Indonesian army.
Despite four years of peace, it says there is still deep suspicion among the military that the old independence fighters have not changed their goals.
Many former rebels are now running for parliament under the terms of the peace deal, and many in both Aceh and Jakarta are worried that GAM's new political party, The Aceh Party - if successful - will threaten Indonesia's unity.
The report says there is little evidence for that, but what is worrying is the lack of accountability in the province.
The police have been "singularly ineffective" it says, with the result that the army has moved into the vacuum and become the dominant security force in the province.
That is in contravention of the peace agreement, and causes problems in itself as it recreates the atmosphere of the conflict years in Aceh's villages.
Tensions have also been raised by the alleged murders of several Aceh Party members - and the failure to find their killers.
Aceh has now been largely rebuilt after the devastating tsunami of 2004, and the international agencies are preparing to pull out.
The problem is, the report says, that they are now needed more than ever.