A 10-year-old girl has become the latest victim of violence in Aceh, where a four-month-old peace pact between the Indonesian government and separatist rebels is close to breaking down.

Ina Rahmati was shot dead by a stray bullet while her friend Fitriana, 12, was critically wounded in an exchange of gunfire between the Free Aceh Movement (GAM) and police Saturday, the state Antara news agency said Sunday. The children were helping their families pick cucumbers at Cot Uno in Bireuen district.

Aceh police spokesman Sayed Hoesainy said the firefight followed an ambush by separatist rebels on police who were trying to haul their truck out of a ditch. "They [the children] were shot by the GAM rebels who fired their guns blindly," he said. The local GAM spokesman could not immediately be reached for comment.

The province on Sumatra island saw an upsurge in violence last week with almost 20 people killed since Tuesday. International and local peace monitors have been withdrawn from field offices to the provincial capital after attacks and intimidation by pro-government crowds. The government accuses the GAM of numerous violations of the peace pact.

Last Thursday it told troops to be ready to go back to war within five days if necessary, unless disputes over the pact could be settled at a meeting of a Joint Council – the final arbiter.

Separatist rebels said they would refuse to attend any meeting inside Indonesia and proposed Geneva. Mediators from the Henry Dunant Centre were frantically trying to get an agreement between the two sides on a date and venue.

Of the estimated 10,000 deaths in the war since 1976, most have been civilians.