Saturday's bomb attack in Bali has startled many people in the region, who, until now, believed that the threat of terrorism in Southeast Asia was exaggerated. It appears the tragedy in Bali will deeply affect perceptions of the terrorist threat in the region and ways to address it.

There have been warnings for months of a major terrorist attack in Southeast Asia. But the bombing in Bali, a laid-back tourist destination that was considered one of the least likely targets, has stunned the region.

Australian Prime Minister John Howard expressed the feeling Monday at a somber parliamentary session. "It was a terrible reminder that terrorism can strike anyone, anywhere, at anytime. Nobody anywhere in the world is immune from terrorism," he said.

No group has claimed responsibility. But a Singapore-based terrorism expert and author of a recent book on the al-Qaida network, Rohan Gunaratna, says only a few groups could mount such a destructive and well-coordinated operation.

"The only organization that has both the intention and the capability to conduct a professional terrorist attack, as the attack we have seen in Bali, only J.I., Jamaah Islamiah, al-Qaida's Southeast Asia network, can conduct an attack of this scale and magnitude," he said.

Singapore, Malaysia and the Philippines, as well as the U.S. and Australian governments, have warned that international terrorist cells are operating in Indonesia. But the Indonesian government, because of domestic political pressures, has been reluctant to move against such groups, saying there was no evidence.

A veteran correspondent in Indonesia for The Christian Science Monitor newspaper, Dan Murphy, says he thinks the proof is now undeniable. "The government of Indonesia has been presented with incredibly stark evidence of its failure, so far, to deal with a massive problem. And it's a problem they probably still do not have the necessary political will and internal cohesion to address," he said.

Indonesian President Megawati Sukarnoputri has pledged to bring the perpetrators to justice, and the Indonesian government has launched a major investigation.

Terrorism expert Rohan Gunaratna believes the Megawati government will be obliged to take action. "The attack in Bali should mount significant pressure on Indonesia to move against these groups. Australia, especially, is likely to mount sustained pressure, because of the huge loss of Australian lives," he said.

Experts say, however, that a major crackdown on suspected terrorists is likely to severely test President Megawati, politically. They say it could cause a backlash from Indonesians, who sympathize with the Islamist cause, and from nationalists, who would see it as subservience to the West.

A security analyst with Honolulu's East-West Center, Richard Baker, says, nevertheless, President Megawati and her government must act decisively. "If they were simply unable to find any plausible connections with groups, or individuals, who might be the perpetrators, they will simply look incompetent in the eyes, both of the world and their domestic opponents.... So, this is a really, really tough situation for them," he said.

Mr. Baker says there are no easy answers. But, he says, it is also a situation, in which the president can rise to the challenge, as she has done in the past, when high moral issues were at stake.