Indonesia has missed a deadline to pass a law granting autonomy to Aceh under a peace pact with separatists but both sides say the delay would not derail the process.

The pact signed last August by the government and the Free Aceh Movement (GAM) called for a law granting Aceh partial self-rule by March 31.

Ferry Mursyidan Baldan, chairman of a parliamentary committee debating the bill, said lawmakers needed more time.

"We have said all along that there's no way we can finish the discussion on March 31. We won't be able to finish discussing a bill in one month, let alone one dealing with an issue as big as Aceh," Baldan told AFP.

"It won't undo the the process that has taken place in Aceh. We are doing our best and this bill is a priority," he said.

Baldan said contentious issues included relations between the central government and the Aceh government, revenue-sharing from the region's natural resources, and the participation of independent candidates in local elections.

A GAM spokesman, Teuku Kamaruzzaman, said the delay was justified and did not consider it a blow to the peace process. "There are many issues that need to be discussed bit it is not reasonable to expect them to finish today," he told AFP.

A report by the International Crisis Group think-tank warned that the law had been diluted by the home affairs ministry and that the toughest times were ahead for the peace accord.

The GAM agreed to drop its demand for independence in return for – among other concessions – the right to form local political parties, which are banned elsewhere in Indonesia to discourage separatism.

Nationalist lawmakers say Jakarta may have gone too far in its concessions, but they have insufficient numbers to block the bill.