Aceh's freedom fighters have been battling for the province's independence for nearly three decades.
Gam rebels are fighting for Acehnese independence
The Free Aceh Movement (Gerakan Aceh Merdeka, or Gam) was founded on 4 December 1976 by Hasan di Tiro - a descendant of the last sultan of Aceh.
The group has grown from an initial membership of just 150 rebels to a military strength now estimated at between 3,000 and 5,000.
While Aceh has a higher concentration of Muslims than the rest of Indonesia, Gam is not seeking to establish a fundamentalist Islamic state. Its argument is more about history than religion.
Gam maintains that when the Republic of Indonesia was formed in 1949, the Kingdom of Aceh should not have been included in the package, since, unlike the rest of the territory, it was never formally under Dutch colonial rule.
The rebels claim the Acehnese people were not consulted about the decision to become part of Indonesia, and are therefore fighting for a return of the province's sovereignty.
That struggle has been fuelled by a perception that the Indonesian government is not fairly sharing the province's considerable natural resources with Aceh's citizens.
ACEH: KEY FACTS
Province on the north-western tip of Sumatra
Higher percentage of Muslims than other parts of Indonesia
Gam rebels have fought decades-long separatist campaign
Internationally-brokered peace deal brokered in Dec 02 but collapsed in May 03
Year-long military crackdown weakened Gam, but failed to capture senior members
Reported abuses of civilians by the Indonesian military have helped stoke tensions still further.
Although its leadership is now largely in exile in Sweden - where some senior Gam officials have been living since the early 1980s - the separatist organisation still enjoys a high level of public support among the Acehnese population.
Since Gam's inception, the rebels have conducted guerrilla-style attacks throughout Aceh, targeting Indonesian security forces.
The military has responded by trying to flush out the rebels from their mountain strongholds.
In the early 1990s, thousands of troops poured into the province to crack down on the rebels, but they failed to crush the insurgency.
Over the years, there have been various attempts by both sides to bring an end to the violence - which has so far claimed an estimated 10,000 lives, many of them civilian.
In December 2002 the government and Gam agreed to a peace deal, which was initially heralded as the breakthrough needed to end the deadlock.
Under the plan, Jakarta said Aceh could have free elections and a partially autonomous government, which would keep 70% of the revenue generated from the province's oil reserves.
In return, the rebels were asked to abandon their claims for complete independence, and hand in weapons.
But Gam's main goal is Acehnese independence, which Jakarta is extremely unlikely to grant - a fact that was never fully addressed in the peace deal.
Cracks soon appeared in the agreement. The rebels were supposed to gradually give up their weapons, while the Indonesian military were expected to withdraw to defensive positions. Neither side fulfilled their part of the bargain.
GAM'S EXILED LEADERSHIP
Hasan di Tiro - Founder and leader of Gam
Malik Mahmood - known as Prime Minister inside Gam
Zaini Abdullah - Gam's chief negotiator ( also referred to as Health/Foreign Minister)
Bakhtiar Abdullah - spokesman for Gam's exiled leadership
Negotiations finally broke down in May 2003.
The government then immediately launched an all-out military offensive, imposing marital law in the province and sending tens of thousands of troops into Aceh to keep control.
The security situation was finally downgraded to a civilian emergency in May 2004, but the military campaign still continued.
Even Gam's exiled leadership was affected. For years the Indonesian government had been putting pressure on Sweden to either extradite or prosecute senior Gam leaders in Stockholm, for crimes against the Indonesian state.
In June 2004 Malik Mahmood, Zaini Abdullah and Gam founder Hasan di Tiro were arrested by Swedish police on suspicion of "crimes violating international law".
All three were soon released, however, after a Stockholm court decided that there was not enough evidence to keep the men in custody.
Effects of the tsunami
The result of the ongoing conflict in Aceh is that for the last 30 years, the province's citizens have been living in a low-level war zone - largely isolated from the rest of the world.
Foreigners - including aid workers and journalists - have not been allowed into the region for some time, and accurate reports of the situation have therefore been hard to obtain.
The huge tsunami could affect the dynamics of the separatist conflict
Since the 26 December tsunami, however, all that has changed.
International groups have been pouring into Aceh to provide aid to the devastated coastal regions, and both the government and Gam have declared a ceasefire to help aid get through to survivors.
It remains to be seen what longer term effects the tsunami disaster will have on the separatist conflict.
The government may feel under pressure to open some kind of communication channel with the rebels, and Gam is also likely to feel the need for a conciliatory gesture.
Aceh's beleaguered people have suffered one of the worst natural disasters in living memory, and the last thing they need is a renewal of hostilities between Gam and the Jakarta government.