Blast proves attacks are a matter of where and when, not if

The Australian embassy bombing underlines what terrorism experts have long warned - that hundreds of arrests have failed to neutralise the extremist group Jemaah Islamiah.

Southeast Asia's top terrorism researchers believe more attacks will take place whenever the opportunity arises and that all cities are vulnerable.

Analysts at the Institute of Defence and Strategic Studies in Singapore, Rohan Gunaratna and Andrew Tan Tian Huat, said they were not surprised by the car bombing.

'We were all expecting an attack,' said Dr Gunaratna, a former investigator with the United Nations' Terrorism Prevention Branch and chairman of the North Atlantic Treaty Organisation's working group on terrorism.

He warned that preparedness must be maintained at the highest level throughout the region, but it was impossible to prevent attacks.

'This attack took place because the opportunity was there,' said Dr Gunaratna, the author of Inside Al-Qaeda: Global Network of Terror, a study of the international terrorist movement to which Jemaah Islamiah is closely linked.

'It wasn't because of the presidential election in Indonesia later this month or Australia's general elections next month - it was because the circumstances were opportune.'