"That (self government) is the main thing on the table," he told Reuters in Helsinki where peace talks with the Jakarta government were in a second day. "Of course in the negotiations we go with the tangible things that are on the table."
Indonesia and the exiled GAM leadership were making their second attempt in three weeks to agree on the future of the gas-rich province on the northern tip of Sumatra island, where the conflict has cost more than 12,000 lives.
GAM has previously rejected offers of autonomy, insisting on independence, but the sides were brought together by the December 26 tsunami which hit Aceh especially hard. Almost 240,000 people are dead or missing and more than 400,000 were made homeless.
GAM leaders, who have lived in Stockholm since declaring independence from Jakarta in 1976, said before the current round of talks they were open to all ideas.
"It's huge, it's a fundamental shift of position, and in itself it probably constitutes the single biggest step in the whole process," said Australian academic Damien Kingsbury, who is advising the rebels.
A change in mood was also alluded to by the mediator of the talks, the Conflict Management Initiative (CMI) group led by former Finnish President Martti Ahtisaari, who said the dialogue was positive and constructive.
Earlier on Tuesday the Indonesian military said it would act resolutely against GAM rebels if the peace talks collapsed.
"If peaceful efforts still could not bear results, we advise to not be hesitant in taking firm measures against GAM," the Antara national news agency quoted military chief General Endriartono Sutarto as saying.