Stephen Brown, Stockholm – Swedish police on Tuesday arrested three leaders of an Aceh separatist group which has been fighting Indonesia for independence since 1976, saying they were suspected of "grave breaches of international law."

Two of the exiled leaders of GAM, the Free Aceh Movement, were being held in custody, the Swedish prosecutors' office said. Jakarta, which has long lobbied Sweden to curtail their activities, welcomed the move.

About 10,000 people, mostly civilians, have died in the fighting between GAM and government troops in the western-most province of the vast Indonesian archipelago.

Jakarta named the three as Hasan Tiro, Zaini Abdullah and Malik Mahmud, who is considered by GAM as Aceh's exiled prime minister. It did not specify which two were in custody.

The Indonesian foreign ministry issued a statement hailing Sweden's "steadfast commitment" to ending "armed rebellion, acts of violence, and acts of terrorism perpetrated by GAM in Aceh and other regions in Indonesia."

Indonesia troops launched an offensive and imposed martial law in Aceh, an oil and gas-rich province on the northern tip of Sumatra island, after peace talks collapsed in 2003. Martial law was lifted this May but there are still 40,000 troops there.

US-based Human Rights Watch said in a report in December the military was waging an extensive campaign of extra-judicial killings, kidnapping and torture in Aceh – a report Jakarta dismissed as "ill-informed and one-sided."

Sweden granted the GAM leaders asylum in the late 1970s. After years of pressure from Jakarta a team of Swedish court investigators including a chief prosecutor went to Indonesia in March to investigate Indonesia's allegations.

GAM spokesman Bakhtiar Abdullah told Reuters in a recent interview in Stockholm that they had taken the precaution of hiring a lawyer after the prosecutors' trip to Indonesia but that they still believed "there is justice and law in Sweden."

Sweden's foreign ministry, asked if Stockholm had yielded to Indonesian lobbying over GAM, said prosecutor Thomas Lindstrand had seen the situation in Indonesia for himself and was acting as "an independent member of the judiciary."

Indonesia goes to the polls in July to choose a new president, with policy on Aceh a campaign issue.

[Additional reporting by Patrick Mcloughlin and Simon Johnson in Stockholm and Jerry Norton in Jakarta.]