Sept. 30 (Bloomberg) -- The likelihood that terrorists will detonate a nuclear weapon poses the greatest risk to world security, surpassing proliferation threats from Iran and North Korea, United Nations atomic chief Mohamed ElBaradei said.

``There is a lot of interest on the part of extremist groups to obtain nuclear material,'' ElBaradei, director-general of the International Atomic Energy Agency, said at a scientific forum today in Vienna during the annual conference of the 145 nations in the IAEA. ``It's the No. 1 security threat right now.''

The IAEA, established in 1956 under the slogan ``Atoms for Peace,'' said it's becoming easier for groups and countries to access nuclear secrets because detailed bomb-making plans have been circulated electronically. Nuclear-armed terrorists are more dangerous than governments with atomic weapons because they don't have the same decision-making restraints, according to ElBaradei.

``The rules of deterrence don't apply to them,'' said the Egyptian diplomat, who won the Nobel Peace Prize in 2005. ``If they get it, they will use it.''

The IAEA has recorded 18 attempts to sell bomb-grade uranium and plutonium to black-market intermediaries since 1993. During the same period, the agency has tracked more than 1,300 incidents involving less-potent nuclear material that may be used to spread radioactive contamination.

``There is a possibility that the seized material was only a sample of larger quantities available,'' IAEA officials who maintain the agency's Illicit Trafficking Database said Sept. 26 in a statement. ``These materials continue to pose potential security risks.''

Radiological Attack

A radiological attack on Washington could inflict economic damage of as much as $107 billion, according to Igor Khripunov, a former Soviet diplomat who runs the Center for International Trade and Security in Athens, Georgia.

North Korea and Iran, along with Saddam Hussein's Iraq, were the countries that President George W. Bush described in 2002 as an ``axis of evil.'' The U.S. accuses Iran of supplying arms to terrorist organizations.

The Persian Gulf nation, which is under three sets of Security Council sanctions for its refusal to halt the enrichment of uranium, says it wants nuclear technology to generate electricity. The U.S. and its allies accuse the government in Tehran of harboring a secret atomic weapons program.

``Influence, power and an assurance against attack,'' are what drives countries to develop nuclear weapons, ElBaradei said. ``Scores of countries'' have the technical know-how to develop nuclear weapons programs, he said.

ElBaradei appealed to the IAEA's 145 members to boost the agency's $16.5 million budget to combat nuclear terrorism. About 90 percent of the budget is restricted funding provided by the member states for specific projects, the IAEA chief said.

To contact the reporter on this story: Jonathan Tirone in Vienna at jtirone@bloomberg.net.

Last Updated: September 30, 2008 08:25 EDT