"Nuclear terrorists" can strike anywhere, the head of the UN atomic watchdog warned Monday at the start of a week-long ministerial conference on preventing misuse of radioactive materials and attacks on facilities.

"Ensuring effective nuclear security is important for all countries, including those which possess little or no nuclear or other radioactive material," International Atomic Energy Agency chief Yukiya Amano said.

"Terrorists and criminals will try to exploit any vulnerability in the global nuclear security system. Any country, in any part of the world, could find itself used as a transit point. And any country could become the target of an attack," he said in Vienna.

Countries all over the world have stepped up their investment in nuclear security with support from the IAEA, and have been working to reinforce staffing levels with more than 10,000 police, border guards and other specialists trained in the past six years, Amano said.

The IAEA has given countries over 3,000 instruments for detecting nuclear material and this year provided radiation detection equipment and other assistance to Brazil during the Olympic and Paralympic Games in Rio de Janeiro.

This year, the IAEA also hosted the International Conference on Computer Security in a Nuclear World looking at the growing issue of cybersecurity as the reliance on digital systems within nuclear facilities grows.