Whether they strike in Bali, London or Tel Aviv, suicide bombers create fear and mayhem. But there is now an even more frightening prospect - a terrorist attack using mass-casualty weapons.
Concerns that such weapons could be used against civilian populations may sound like the stuff of science fiction. Yet many Asian and western officials, and arms-control experts, believe that a chemical, biological, radiological or nuclear attack somewhere in the world in the next decade is highly probable. These deadly materials and the technology to make them are becoming more widely available through trafficking, dispersal of scientific and industrial knowledge via the internet, and the spread of nuclear weapons beyond the states known or thought to have them.
Richard Lugar, chairman of the US Senate Foreign Relations Committee, commissioned a survey of 85 arms-control and national-security experts to assess the danger, and the results were published in June. Asked to rate the possibility of a chemical, biological, radiological or nuclear attack on any nation, the respondents put the likelihood of one of the four happening at 50 per cent over five years and 70 per cent over 10 years. They saw an attack with a radiological, or 'dirty' bomb - combining a conventional explosive such as dynamite with cancer-causing radioactive material - as the most likely form of attack, with a risk of 40 per cent over the next decade.
The International Atomic Energy Agency (IAEA), the United Nations' nuclear watchdog, has outlined four possible terrorist scenarios involving nuclear weapons or radioactive materials. The first, theft of a nuclear bomb, is considered highly unlikely because arsenals are closely guarded. But should it happen, the consequences would be potentially devastating. Experts have estimated that between 500,000 and 2 million people could be killed if a one-megaton nuclear bomb exploded in a major city.
The second possibility is for terrorists to acquire enough plutonium or highly enriched uranium, along with the sophisticated equipment and expertise needed to build and detonate a crude nuclear explosive device. This, too, would be difficult, though not impossible, for an extremist group without state support and protection.
A third threat that concerns the IAEA is a terrorist attack on, or sabotage of, reactors or other nuclear facilities - contaminating surrounding areas with radioactivity. Nuclear power plants and fuel facilities are generally considered to be tightly secured. But the same cannot be said for more than 270 research reactors that the IAEA says are currently in operation in at least 56 countries, many of them developing nations. A lot of these reactors run on highly enriched uranium.
Just last week, the IAEA reported that illicit trafficking of nuclear and other radioactive substances was on the rise, raising the prospect of terrorists acquiring widely used isotopes like Cesium-137, Americium-241 or Cobalt-60 to put into a 'dirty' bomb. Member states reported 121 trafficking incidents to the IAEA last year, about half of them involving criminal activity. It was the first time the annual tally had risen since 2000.
The IAEA report follows a region-wide check in the past year by the Australian Nuclear Science and Technology Organisation. It found unsecured cobalt in two unidentified Asia-Pacific countries.
A radiological bomb may not be a real weapon of mass destruction when compared to a nuclear explosion, but it would certainly be a weapon of mass disruption in any city. There would be public panic over radioactivity; decontaminating affected areas would take a long time; and the economic cost could be huge.
Michael Richardson is a visiting senior research fellow at the Institute of Southeast Asian Studies in Singapore. This is a personal comment