"Australia's Foreign Minister Alexander Downer said there were "preliminary indications" that an Islamic radical group could be behind the attack.

"We have been very concerned about terrorist organizations operating in southeast Asia , including Indonesia, organizations such as Jemaah Islamiah, and there are at least preliminary indications that one of those types of organizations is behind this," Downer told CNN.

Jemaah Islamiah -- a group that authorities believe is al Qaeda's network in Southeast Asia -- is blamed for a September 23 grenade explosion near a U.S. Embassy warehouse in Jakarta.

International terrorism expert Rohan Gunaratna told the Australian Broadcasting Corporation late Sunday that Jemaah Islamiah, or JI, was the most likely culprit for the Bali attack."