Chris McCall, Jakarta – Troubled Aceh prepared a hero's burial for its slain son Jafar Siddiq Hamzah yesterday as fellow human rights activists around the world condemned his murder. They said the killing was part of a pattern of growing intimidation of rights workers in the Sumatra province.

As his family waited in a Medan hospital for doctors to release his body, the New York-based pressure group he founded and led vowed to continue his struggle to expose human rights abuses.

"The International Forum for Aceh will continue the work which Jafar guided us in doing: the documentation of human rights violations occurring in Aceh and the steadfast defence of the people of Aceh and of Indonesia from the terrorist tactics of militarised groups which are increasingly targeting innocent civilians and human rights activists," said spokesman Robert Jereski.

Jafar vanished on August 5 in Medan, Sumatra's main city and entry point to Indonesia for visitors heading for Aceh to the north. This week, five mutilated bodies were found in woods west of the city and family members suspected that one of them was Jafar. The United States yesterday urged the Indonesian Government to track down Jafar's killers.

He is to be buried in his birthplace, Lhokseumawe – Aceh's main economic centre and one of the most violence-riddled areas of the province.

Thousands have died in Aceh's long-running separatist war – with reports of at least 24 more killings within the past 48 hours. Amnesty International cited a series of other recent disturbing cases in Aceh as it called for a thorough investigation of the murder.

The London-based group said there had been increased threats and intimidation towards rights workers in recent weeks. It cited a 24-year-old volunteer named Amrisaldin who it said had been arrested by the military this week. It accused security forces of breaking laws they were supposed to defend.

"His arrest is apparently connected to his work in South Aceh with people displaced by ongoing violence between the security forces and the armed opposition group," said Amnesty. "Anonymous telephone death threats have been received by activists in Banda Aceh and three Acehnese staff members of an international humanitarian agency were assaulted by members of the Police Mobile Brigade [Brimob] on 28 August."

Sidney Jones, who until recently headed the United Nations' human rights team in East Timor, paid a personal tribute. "Jafar was a friend, a colleague and one of the most dedicated human rights defenders I've ever known," said Ms Jones. "The most fitting honour to his memory will be to bring to justice not only his killers but those responsible for the thousands of disappearances that have taken place in Aceh over the past decade."

Ms Jones, Asia director of Human Rights Watch, said the Indonesian police must be incompetent or implicated for failing to solve so many disappearances.