JAKARTA, June 22, Reuter - A wave of killings by mysterious armed rebels in Indonesia's strictly Moslem northernmost province of Aceh is fast becoming a major source of anxiety to the government, analysts said on Friday.

Nobody is sure who the rebels are or what they want.

Drug tycoons, military deserters and Libyan-trained insurgents are all talked of as possibilities, analysts said.

Most likely, the rebels are ordinary Acehnese tired of economic discrimination by their rulers in Java, they said.

The present spate of killings in the northern Sumatran province began in April. At least six people have died and many others have been injured, the military said.

Human rights groups said they have received unconfirmed reports of 72 casualties among the military alone.

"What is certain is that (the rebels) are quite active and quite violent and that they have really got the Indonesian government concerned," one political analyst said.

"Of course we're worried, that's clear. What is not clear is who is involved or why," said Ismail Hasan Metareum, a member of parliament for Aceh.

The regional military commander for Aceh Pramono told reporters this week that the violence, by a group he called GPK -- the Security Disturbing Movement -- had reached intolerable limits.

"ABRI (the armed forces) and the government are determined not to tolerate the ideas, attitudes and actions that disturb security," he said. "ABRI and the people will do whatever it takes for the sake of continued development in Aceh."

Standard ABRI-issued weapons used in some attacks indicate army deserters form part of the group, sources in Aceh said.

The province has a history of violent opposition to outside authority. In addition, its heartland contains thousands of hectares of marijuana fields.

"It could be just common criminals running drugs and calling themselves separatists. Or it could be that people with genuine separatist convictions are getting into the drug trade to finance weapons," a diplomat said.

There are also rumours, originating from statements by an army officer and since denied by ABRI, that a number of Acehnese recently returned from Libya may be involved.

"It's possible, but I think this would be happening, Libya or no Libya," a diplomat said. "The connection is pretty unclear."

The violence is most probably the work of locals who resent that Jakarta-funded development projects benefit Javanese bureaucrats and migrant labour most, analysts and Acehnese said.

Most of the confirmed attacks have centred around the northeast, which with its huge liquefied natural gas (LNG) and fertiliser plants is in stark contrast to the undeveloped jungles of the rest of the province.

"A lot of people are not satisfied with Jakarta's way of developing the region. They feel the benefits of oil exploration, the LNG plant, et cetera, are not going to them, that most of the people remain poor," an Acehnese civil servant said.

Several attacks have been made on areas that are home to Javanese who have moved to the province in a government programme to resettle people from crowded Java in underpopulated areas.

"Aceh people are very proud of being Acehnese. They have a history as the toughest strugglers against the Dutch in colonial times. The province is rich in natural resources and they want exclusive rights to them," the civil servant said.

The rebels are supported by an older generation that feels the Java-centric development is swallowing the identity of the militantly Islamic province, one analyst said.

"Perhaps there are only a few GPK who are actively carrying guns and isolating themselves in the jungle. But the rest are probably the man you meet on the street, a student who in his daily life looks busy with his books or a friendly civil servant," one Acehnese said.