Helsinki – Aceh rebels and Indonesian government delegates have made a "breakthrough" at peace talks on the tsunami-ravaged province, and will continue negotiations in Finland May 26-31, the Finnish mediator said Saturday.

Former President Martti Ahtisaari made the announcement after the end of the third round of negotiations which he said were "held in a positive and constructive atmosphere."

The parties had been meeting since Tuesday behind closed doors at a mansion outside Helsinki for talks mediated by Ahtisaari's Crisis Management Initiative.

"I would like to describe this as a breakthrough. We are now looking at the nitty gritty... [at] difficult issues they need to consult on both sides and come back," Ahtisaari said at a news conference. "We have moved to a very substantive discussion on the issues," he said.

Ahtisaari declined to take a stand on what regional organizations could be involved in monitoring any peace agreement and again ruled out the involvement of the UN.

The two sides decided to end the third round of talks a day earlier than planned.

The Free Aceh Movement, which claims about 5,000 fighters, has been struggling for 27 years for a separate homeland in the oil- and gas-rich region. More than 12,000 people have been killed.

Ahtisaari said the two sides had agreed to do their utmost to restrain their security forces in the field during the negotiations, which would seek to define the framework for Aceh's local administrative structure and the details of providing amnesty to rebels.

On Friday, Indonesian Information Minister Sofyan Djalil said the two sides had found "a lot of common understanding." "The intention and goodwill is there. Both parties are looking for a peaceful settlement, and that's the most important thing," he added.

The talks have centered on limited self-government for the province and the integration of the rebel movement into society.

Indonesian President Susilo Bambang Yudhoyono said Jakarta would never allow Aceh province to separate from the rest of Indonesia, but added that a government plan to give the region a greater say in running its affairs must be implemented.

The tsunami disaster brought the two sides to the negotiating table, with the first round of talks held in January.