A riot at a police detention centre near Indonesia's capital left five officers and a prisoner dead and another officer held hostage on Wednesday. The Islamic State group said its fighters were involved but authorities blamed the violence on a food fight.
Negotiations were underway for the release of the hostage, said national police spokesperson Muhammad Iqbal.
The riot erupted in Depok, on Jakarta's southern outskirts, where four days earlier police arrested three Islamic militants they say planned to attack the headquarters and other police stations in the same town.
The Islamic State group's Amaq News Agency said its fighters took part in the riot late on Tuesday.
"The claim by ISIS was not true. This incident was just triggered by a trivial thing, about food from families," Iqbal told reporters outside the headquarters of the elite Mobile Brigade police in Depok.
He said an inmate who was fatally shot after grabbing weapons and threatening officers. A counterterrorism investigator said four police officers were wounded and were being treated at a hospital.
Authorities said the riot began when an inmate shouted and banged on the walls to protest a delay in getting food from his family that was being checked by officials. Other inmates broke into the ammunition room and seized long-barrelled weapons, leading to a shootout with counterterrorism officers.
Indonesia, the world's most populous Muslim nation, has carried out a sustained crackdown on Islamic militants since the 2002 Bali bombings by Jemaah Islamiyah network that killed 202 people, mostly foreigners.
The network was neutralised following the arrests of hundreds of its militants and leaders. But new threats have emerged recently from Islamic State group-inspired radicals who have targeted security forces and local "infidels" instead of Westerners.
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