Updated

U.S. counterterrorism officials believe that a shadowy Indonesian cleric with links to Al Qaeda played a leading role in a thwarted effort to bomb at least one American embassy in Southeast Asia on the anniversary of Sept. 11.

Hambali, whose real name is Riduan Isamuddin, is the operations chief of Jemaah Islamiyah, a regional Islamic extremist network that receives support from Al Qaeda, according to U.S. officials who spoke on the condition of anonymity.

U.S. officials have declined to specify the target or targets of the Sept. 11 anniversary operation or to detail how the plots were averted. Hambali's precise role in the attack has not been laid out either, but terrorism officials suspect him of organizing other terrorist attacks as well.

Counterterrorism officials learned critical aspects of the bombing plot from an Al Qaeda operative who was captured by Indonesian authorities in June. His information led to the closure of embassies in Indonesia, Malaysia, Cambodia and Vietnam. That day, the Philippine government released a letter from U.S. Assistant Secretary of State James A. Kelly warning that Al Qaeda members were prepared to launch truck bomb attacks in the region and that intelligence indicated "imminent threats to U.S. Embassies."

The prisoner, Omar al-Farouq, was turned over to U.S. authorities after his capture. He recently began talking to his interrogators. Al-Farouq and Hambali are believed to have been close associates, with al-Farouq serving as liaison between Jemaah Islamiya to Al Qaeda's senior leadership.

His interrogation has provided a clearer picture of Jemaah Islamiyah, a group U.S. officials say has a twofold purpose: to create an Islamic state in Southeast Asia and to conduct acts of terrorism against U.S. interests.

Jemaah Islamiyah resembles Al Qaeda in organization and, like Al Qaeda, operates across international boundaries. The group has cells in Indonesia, Singapore, Malaysia, the Philippines, Myanmar and Thailand.

This is unlike many other groups affiliated with Al Qaeda, many of which are focused on overthrowing the government of a single country.

Leadership of the group is split between Hambali, who handles operations, and Abu Bakar Ba'asyir, another Indonesian cleric who denies links to terrorism but is believed to be the group's spiritual leader, according to U.S., Singaporean and Malaysian officials. The group has sent people to Usama bin Laden's Afghan camps and received money from Al Qaeda.

Hambali's whereabouts are unknown. According to Singapore's Home Affairs Ministry, Hambali also gave the orders to Jemaah Islamiyah operatives who were arrested in December 2001 in connection with plots to bomb the U.S. Embassy in the city-state and American naval targets.

In addition, Hambali has been linked to two Sept. 11 suicide hijackers. He is believed to have arranged the January 2000 meeting of Khalid al-Mihdhar and Nawaf al-Hazmi with a senior Al Qaeda operative, Tawfiq Attash Khallad, one of the masterminds of the USS Cole bombing later that year. The subject of the meeting remains a mystery.

Abu Bakar Ba'asyir lives openly in Indonesia, despite entreaties from Malaysia, Singapore and the United States to authorities there to arrest him. Indonesian officials say they have no evidence to arrest him, but American officials suggest the Indonesian government fears a public backlash if the popular cleric is detained.

Ba'asyir denies links to terrorism and that Jemaah Islamiyah exists, but U.S. counterterrorism officials allege he founded the group in 1989 and maintains knowledge of the group's operations.

In a recent interview with The Associated Press, he challenged the United States to make its case against him and warned that jailing him would anger Muslims.

"I am not fighting against the American people but against the U.S. government," he said. "The government and the Jews are fighting against Muslims. It's part of a crusade by America to attack Islam. The United States hates me because I struggle in the name of Islam."