Finnish mediators are to draw up an outline of a long-sought peace deal between Aceh separatists and the Indonesian government after winding up a fresh round of talks, they said.

Former Finnish president Martti Ahtisaari, a career diplomat who mediated the talks, told reporters that his Crisis Management Initiative had been asked to prepare "basic documents that could form the basis for the eventual agreement." The documents would be sent to both sides for consideration before the next round of negotiations in the Finnish capital starting July 12.

They would form a basis of discussion for those talks, which officials hope could reach a deal to end one of Asia's longest-running conflicts, which has left more than 12,000 people dead over three decades.

Ahtisaari said he was optimistic that an agreement could be reached between the Jakarta government and representatives of the Free Aceh Movement (GAM).

"If I didn't believe there was a chance to find a negotiated settlement I would blow the whistle immediately," he said. "I think we have reached a stage where we can talk through the most difficult issues, which is the only way we can reach a deal," he said.

Aceh, a province on the northern tip of the island of Sumatra, has been a battleground since 1976 when GAM began its campaign for independence, angered by what it said was Jakarta's exploitation of oil and gas resources.

Any peace agreement would have to include the thorny issues of "decommissioning of arms of GAM and militias plus the withdrawal of national forces and police," Ahtisaari said.

Indonesian officials attending the talks were also upbeat about the possibility of a deal. "Hopefully after one or two more meetings the settlement of the issue of Aceh within the republic of Indonesia will be all set up," Communications Minister Sofyan Jalil said.

GAM, which has already given up its demand for full independence in exchange for self-government, agreed that the discussions had been "positive and constructive".

But spokesman Bakhtiar Abdullah stressed that there were still many outstanding issues. He cited the "timing of elections [in Aceh], establishing of political parties and the withdrawal of the special autonomy law to be replaced by self-government."

The six-day meeting in Helsinki focused on self-government, political participation, economic arrangements, amnesty and reintegration into society, human rights and justice, security arrangements and how to monitor any peace deal that might be reached.

Any agreement would ease reconstruction in the troubled province after the December 26 Indian Ocean undersea earthquake off the coast which triggered tsunamis that killed 128,000 people in Aceh alone.

Four rounds of talks have been held in Helsinki since January. But despite the positive atmosphere coming out of the talks violence has continued on the ground.

On Monday, Indonesian soldiers shot dead three more separatist rebels during a raid in the northern Aceh area of Bireuen, a stronghold for rebels.

Ahtisaari said he had appealed to the two sides "to do their utmost to restrain their parties in the field during the negotiation process".

An EU team of experts was invited to the latest round of talks in Helsinki to discuss a possible role in monitoring any peace deal.

Ahtisaari said there was "no commitment from the EU side" yet, but stressed that any observers sent to the region would monitor the "undertakings in the agreement" and not be peacekeeping forces.

The Finnish diplomat also underlined that any peace deal had to include an agreement on political participation in the region allowing for the creation of new parties. The Aceh separatists are unable to meet the existing requirement of nationwide representation.

"If you cannot solve this issue, you cannot have an agreement because the existing parties are not an option," he said.