Chris Brummitt, Jakarta – Posters plastered around Jakarta by the Islamic Defenders Front are clear enough: "Burn the nightspots that refuse to close for Ramadan," reads one. Another promises to destroy whoever "soils the holiness" of Islam's fasting month.

Sitting cross-legged in Islamic Defenders Front headquarters, the part-time preacher who heads the group's anti-vice squad strikes a more persuasive tone, but his message is the same.

"We let the owners of the discos know in advance. We write them letters," said Siroj Alwi, who wears a white Muslim tunic with military-style epaulets. "But if they refuse to shut, we close the places by force."

Attacks by Muslim groups on bars, discos, brothels and gambling joints have intensified since the beginning of Ramadan two weeks ago. Armed with swords and wooden poles, the gangs have smashed audio equipment, furniture and bottles of alcohol worth tens of thousands of dollars. Dozens of people were injured when waiters and thugs hired by the establishments resisted the raiders.

During Ramadan, Muslims are not supposed to eat or drink during daylight hours. Family gatherings, prayers and meditation are encouraged after dark. About 90 percent of Indonesia's 210 million people are Muslim, making it the world's most populous Islamic nation.

The national constitution, however, provides for a secular government and promotes tolerance, and many of Indonesia's Muslims are influenced by pre-Islamic animistic beliefs and practices. As a consequence, official observance of the fasting month is less rigid than in neighboring Malaysia and Brunei.

Since coming to power 14 months ago, President Abdurrahman Wahid has urged harmony among different faiths. Wahid, a revered Muslim scholar who formerly led the nation's largest Muslim organization, often addresses gatherings of minority Christians and Hindus and has railed against religious fundamentalism.

But facing increasing pressure from Muslim groups, he has made some concessions. Most notably, he has agreed to introduce Islamic law, or Sharia, in the far western province of Aceh as a way of diluting support for separatists who want to establish an independent Muslim state. Thousands have been killed in a 25-year guerrilla war there.

Separately, Jakarta's own city administration also has bowed to the sensitivities of some stricter Muslims. It has ordered the closure of most nightspots during Ramadan. Many remained open, however, with their owners saying the rules are unclear.

The Islamic Defenders Front, which claims 70,000 members in Jakarta and branches in 19 provinces across Indonesia, says its attacks on nightspots are justified by verses in the Quran, the Muslim holy book.

Some Muslims also allege that police and officials accept payoffs from nightclub owners.

But critics say extremist groups are misinterpreting Islam for their own ends. "They are spoiling the image of Islam as a peaceful religion," said Nadjamin Ramli, chairman of the youth wing of Muhammadiyah, one of Indonesia's largest Muslim organizations.

Owners of the establishments say that if they suspend business they will not be able to pay their workers' salaries. "The staff need to eat," said Tegas Prita Soraya, who co-owns a salsa bar that was attacked recently. "Where will we get the money to pay them?"