The Indonesian government and Aceh separatists will sign a formal peace accord next month in an effort to end a 30-year conflict that has killed about 15,000 people, Indonesian and Finnish officials said Sunday.

A basic agreement, reached Saturday in Helsinki, Finland, covers issues of law, human rights, security, and amnesty for the rebels and their reintegration into society, according to former Finnish president Martti Ahtisaari, who mediated the talks, the Kyodo news service reported.

Details of the deal are not expected to be released before the signing ceremony Aug. 15 in Helsinki. The agreement must be approved by the Indonesian parliament.

On Monday, presidential spokesman Dino Patti Djalal called the breakthrough "important" given the high degree of doubt that the two sides would be able to achieve a political solution to the conflict.

For the first time, Djalal noted, the rebels have accepted that Aceh is a part of Indonesia. That alone is "very historic and will allow for a conducive political environment for the reconstruction of Aceh," he said.

Leaders of the rebel group, the Free Aceh Movement, known by its Indonesian acronym GAM, had earlier dropped their demand for an independent state.

"The devil is in the details," Djalal said. "If this agreement goes through, then it will be a new political chapter in Aceh."

On Sunday, President Susilo Bambang Yudhoyono in Indonesia repeated the government's refusal to allow the creation of local political parties. According to the state-run news agency Antara, Yudhoyono said: "Even though we are not giving them a chance to set up a political party, the most important thing is how to enable them to have political rights and opportunities to follow the existing political process in the same way as other elements in Aceh do."

Aceh province was the area hardest hit by the Dec. 26 earthquake-driven tsunami, which left an estimated 120,000 people dead in the province. After the disaster, the rebels declared a cease-fire and both sides came under intense international pressure to end the long-running war.

Aceh, a devoutly Muslim province of 4 million people on the northern tip of Sumatra island, is rich in oil, but separatists have argued that it has not been able to exploit its own resources.