Men in black clothes and masks beheaded three teenage Christian girls on Saturday in eastern Indonesia as they walked to school near the Muslim town of Poso, officials said.
President Susilo Bambang Yudhoyono condemned the killings, which he described as "sadist and inhuman crimes", and called an emergency security meeting with his vice-president, as well as military officials and police.
National police spokesman Aryanto Budiharjo said up to six men in black clothes and masks attacked the students in Bukit Bambu village, on the eastern island of Sulawesi. "The perpetrators wore black attire and veils and they used machetes to slash (the victims)," he told reporters in Jakarta.
The three headless bodies of the high school students, dressed in brown uniforms, were left at the site of the attack. Three heads were found at separate locations two hours later by residents. Earlier, a police official in Poso gave a different account, saying two men wearing helmets on a motorcycle attacked the 16-year-old students.
Poso, 1,500 km (900 miles) north-east of the capital Jakarta, is in an area where Muslim-Christian clashes killed 2,000 people until a peace deal was agreed in 2001.