VIENNA: The head of the UN atomic agency warned Monday against complacency in preventing "nuclear terrorism", saying progress in recent years should not lull the world into a false sense of security.

"Much has been achieved in the past decade," Yukiya Amano of the International Atomic Energy Agency told a gathering in Vienna of some 1,200 delegates from around 110 states including 35 ministers to review progress on the issue.

"Many countries have taken effective measures to prevent theft, sabotage, unauthorised access, illegal transfer, or other malicious acts involving nuclear or other radioactive material. Security has been improved at many facilities containing such material."

Partly as a result, he said, "there has not been a terrorist attack involving nuclear or other radioactive material."