The Indonesian military said it has killed 12 separatist rebels in troubled Aceh province.

Soldiers killed eight Free Aceh Movement (GAM) members in a 30-minute encounter at Alam Jeumpa in West Aceh district on Wednesday, said provincial military spokesman Major Zaenal Muttaqin.

Also Wednesday, three guerrillas were killed and three arrested in a military ambush at Mereu in Aceh Besar district, he said. GAM said the 11 were civilians.

The military spokesman said troops killed another suspected rebel at Kampung Blang in North Aceh on Wednesday. A handgun and two home-made bombs were seized.

A rebel spokesman, Teungku Jamaica, said soldiers shot dead a civilian at Simpang Keuramat in North Aceh on Wednesday. The military denied the claim.

Jamaica also said two men were found dead on Wednesday in separate places in North Aceh. They had been arrested a few months ago by soldiers guarding the gas plant of US-based oil giant ExxonMobil, he said.

Police and troops have stepped up offensives against rebels following a recent series of kidnappings, arson attacks and murders which they blame on the separatist movement.

Aceh police said Thursday that at least 50 people had been taken hostage by the rebels over the past four months. Adjunct Senior Commissioner Dadek Achmad said more than 20 of them had yet to be released.

He said the remainder had been freed for ransom amounting to "hundreds or at least tens of million rupiah [thousands or hundreds of dollars]. Otherwise they will execute them [the hostages] mercilessly," Achmad said.

Earlier this month GAM released nine crewmen seized from an oil company supply ship and nine athletes and sports officials. GAM said they were freed after they were found to be civilians and not engaged in military operations.

Top security minister Susilo Bambang Yudhoyono on July 4 said the government wanted to declare a state of civil emergency against what he called "terrorists." But various parties in the province advised him against such a move during his subsequent visit to the energy-rich region on Sumatra island. An estimated 10,000 people have been killed since the revolt for independence began in 1976, more than 600 of them this year.

The military commander in Aceh has asked for 2,000 extra troops. Jakarta said the demand is still being studied pending a review of its overall policy on the province.