JAKARTA — Indonesian troops were on high alert Monday, bracing for a new cycle of sectarian violence in a province where machete-wielding assailants beheaded three Christian schoolgirls and seriously wounded a fourth.

Religious leaders called on their followers to remain calm and to refrain from revenge attacks, reminding them that investigators have yet to determine who was behind Saturday's grisly murders in Central Sulawesi province.

Suspicion has fallen, however, on Islamic militants responsible for a series of attacks on Christians since a peace deal in 2002 ended a bloody conflict that killed as many as 1,000 people from both communities.

National police spokesman Maj.-Gen. Aryanto Budihardjo said there were no key suspects in the killings, and that only six people have been questioned so far, among them the wounded teenager who was being kept under close watch at a police hospital.

He blamed the attacks on "terrorists'' seeking to destabilize the province "just as relations between Muslim and Christian communities were improving,'' and said the perpetrators should not be allowed to plunge the region back into violence.

The attack, which occurred days before the Islamic holiday of Eid al-Fitr at the end of the holy month of Ramadan, has dominated national TV reports and been splashed across the front pages of newspapers.

Many people fear Muslims, flocking to outdoor markets and shops to prepare for the celebration marking the end of the Islamic holy month of Ramadan, could be the target of Christian retaliatory acts.

Preparing for the worst, the government deployed more than 1,500 soldiers and police armed with assault rifles across Central Sulawesi Monday, the large majority of them in the predominantly Muslim town of Poso.

Muslim leaders condemned the weekend killings, but cautioned Monday it was too early to lay blame.

"Until authorities arrest the killers and disclose the motive, it's too early to say this attack was religiously motivated,'' said Syafi'i Ma'arif, leader of Indonesia's second-largest nonpolitical Muslim group Muhammadiyah.

"But I can say the Muslim community is shocked and deeply concerned about the inhumane killing of innocent students,'' he said, adding that the victims deserve justice.

Although President Susilo Bambang Yudhoyono ordered police to track down the killers, Christian residents said Monday they were afraid to leave their homes.

"We are really scared,'' said Noldi, who goes by only one name and lives in the same village as the three slain high school girls. "For the time being we're spending all day and night inside.''

The injured girl, who was in stable condition Monday, said six assailants wearing black veils carried out the attack as the students walked through a cocoa plantation on their way to school just outside of Poso, said the provincial police chief Col. Oegroseno.

The heads of the three victims were found several kilometres from their bodies. Two were left near a police station and another in front of a newly built Christian church.

The Vatican on Sunday called the beheadings a "barbaric'' attack and said Pope Benedict was praying for renewed peace in the region.

Indonesia is the world's most populous Islamic country. Most of its more than 190 million Muslims practise a tolerant version of the faith, but hardline groups are increasingly making inroads.

In recent months, the country's highest Islamic body has issued a fatwa condemning liberal Islamic thought and radical groups have stepped up campaigns to prevent the country's Christian minority from building more churches.

Central Sulawesi, which has a roughly equal number of Muslims and Christians, has been hit by several attacks in recent months.

A blast at a market in May killed 22 people, mostly Christians. A bomb attack on a minivan carrying 11 Christian passengers last week injured one.