Investigators piecing together evidence in the Bali nightclub bombings disclosed Monday the main bomb was made of ammonium nitrate, a compound stockpiled by an Islamic extremist group allied with Al Qaeda.

Though police stopped short of saying the bomb was made and planted by Jemaah Islamiyah, which has been blamed for a series of bombings in Southeast Asia in recent years, the use of ammonium nitrate reinforces suspicions the group was involved.

More than 180 people died in the Oct. 12 bombings, and a U.S. consular official said Monday the dead include seven Americans — two whose remains have been identified and five others who are missing and presumed dead.

Meanwhile, Indonesia's moderate Muslim organizations demanded that authorities crack down against Jemaah Islamiyah and religious extremists, who they said represent a fringe minority of the country's 170 million Muslims.

The demands came amid a continued standoff in the town of Solo, in central Java, between police, who want to question Jemaah Islamiyah spiritual leader Abu Bakar Bashir, and scores of students at his Islamic boarding school.

Bashir, 64, is hospitalized with reported respiratory and heart problems, though police have said they do not believe he is ill. They have made no move to take him by force, but are deployed around the hospital and say they will wait to question him.

For the third day, students from Bashir's school turned out and vowed to prevent him from being taken away. Their determination raised fears of a possible clash if police try to move Bashir to Jakarta.

Bashir is not a suspect in the Bali bombings, but was arrested last week on suspicion of being behind several church bombings in Jakarta on Christmas Eve 2000 that killed 19 people, and in a plot to assassinate President Megawati Sukarnoputri.

The international community had urged Indonesia for months to arrest Bashir as plots and attacks attributed to Jemaah Islamiyah mounted around Southeast Asia. But Indonesia, fearing an extremist backlash, refused until pressure in the wake of the Bali bombings grew too strong to resist.

Former Indonesian President Abdurrahman Wahid, who heads the 40 million-member Nahdlatul Ulama, Indonesia's largest terror group, said in a radio interview Bashir should have been arrested long ago.

"I believe that Bashir is a terrorist," Wahid said. Wahid, who was replaced as head of state by Megawati last year, has been sharply critical of her cautious approach toward radicals.

Megawati signed an emergency decree last week that allows terrorist suspects to be detained for up to six months without charge, but religious moderates have called for even tougher anti-terrorist legislation.

Jemaah Islamiyah is known to have acquired at least four tons of ammonium nitrate, an agricultural chemical that can be made into large car and truck bombs.

More than 100 foreign investigators from Australia, the United States, Britain, France, Germany and Japan have been helping Indonesian police find evidence at the blast site in Kuta beach, a nightclub district popular with tourists.

Investigators said Monday they believed an initial blast at Paddy's pub was caused by a bomb containing no more than 2.2 pounds of TNT. The second, much deadlier, explosion at Sari's nightclub was caused by 110-330 pounds of ammonium nitrate.

A separate bomb near the office of the honorary U.S. consul, which caused no casualties, contained less than a pound of TNT, said Brett Swan of the Australian federal police.

Indonesian police have questioned 70 people but made no arrests and say they do not know whether the bombers remain in Indonesia, an archipelago of 13,000 islands.

Thomas C. Daniels, U.S. vice consul in Surabaya, said Monday that in addition to the seven Americans confirmed or believed dead in the bombings, 45 Americans are listed as missing.

However, he stressed the vast majority of the 45 are unlikely to be victims of the blast. Several nations have large numbers of missing who have not been tracked down since the attack — but that may mean only that they haven't phoned home, or that when they did, their families didn't notify officials.

To narrow down the figures, U.S. officials are telephoning families to ask them to send dental records or fingerprints to check against the remains of the dead.