Jakarta – Indonesia's military claimed partial success on Friday in a four-month campaign to crush rebels in Aceh province but said it needed more time to end the insurgency.

Indonesia put strife-torn Aceh under martial law on May 19 and launched a military campaign to counter rebels from the Free Aceh Movement (GAM) after peace talks failed to end a war that has killed more than 10,000 people since 1976.

"We admit that GAM's force has not been totally paralysed. However, in these four months their strength has been largely reduced compared to before," General Endriartono Sutarto told a news conference.

"We can't pinpoint when we can paralyse GAM. From past examples in the world, dealing with guerrillas can take decades." Asked whether the military wanted to push the government to extend the time-frame for martial law in Aceh, which is scheduled to end in two months, Sutarto said: "That's up to the president." "From our perspective, whatever the decision is, whether it's an extension or an abolition, we hope the momentum we have now can be maintained," he said.

According to latest military estimates issued on Friday, Indonesian troops have killed 839 rebels and captured 989 since May. At the start of the campaign, the military said GAM had around 5,000 members.

The military said 52 soldiers, 11 policemen and around 300 non-combatants have been killed during the offensive, including one foreigner.

Military counts on Aceh are hard to verify, especially after Jakarta issued a decree in June that restricts foreign media coverage and bars all foreigners from communicating with GAM.

Critics also attacked the decree for stipulating that all aid be distributed by martial law administrators and that foreign aid groups not communicate directly with Acehnese without approval from local authorities.

New York-based Human Rights Watch said in a statement on Friday the Aceh offensive may have sparked a humanitarian crisis and warned that without outside assistance local authorities might not be able to distribute food and supplies. The military offensive has prompted tens of thousands of residents to flee their homes.

The HRW statement triggered harsh words from Jakarta. "It's very arrogant for an agency like Human Rights Watch to think that because they can't get access to a certain place like Aceh, because they don't have eyes and ears and mouths therefore the situation there is closed and there must be rights abuses," foreign affairs spokesman Marty Natalegawa told reporters.