Indonesian security forces are patrolling cities in the northern separatist province of Aceh after at least 16 bombs and grenade blasts rocked the area overnight.
Witnesses say Aceh's provincial capital, Banda Aceh, remains quiet as troops patrol the largely empty streets.
A series of explosions Thursday night severely damaged four banks and caused a power blackout for several hours. Local media report that a child was injured in a blast at a badminton court outside the capital.
It remains unclear who is behind the blasts, but authorities suspect separatist rebels from the Free Aceh Movement.
Police also say they are investigating what they believe to be a mass grave in Lhong district in the western part of the province. Officials unearthed 48 badly decomposed bodies, but they do not know who the victims are or how they died.
The bombs and the discovery of the mass grave came just hours after Indonesian President Megawati Sukarnoputri apologized to the people of Aceh for the human rights violations caused by government policies. But the president, in her first state of the nation address Thursday, ruled out any possibility of independence for Aceh.
Human rights groups say thousands of people have died in Aceh in the past decade in fighting between Indonesian troops and members of the Free Aceh Movement. The separatist group declared the province independent of Indonesia in 1976 and has been struggling for recognition of that declaration ever since.
The group says the province is being exploited for its natural resources but little returns have trickled back to its people.
The Indonesian government has recently passed an autonomy law aimed at quelling the secessionist movement in Aceh.