The head of the International Atomic Energy Agency says North Korea poses the world's number one security problem, and the way the international community responds to its nuclear program will be an important precedent.

Mohamed ElBaradei said Friday that North Korea's pursuit of nuclear weapons sends the worst signal to the would-be proliferators that, if they accelerate their weapons programs, they will be "immune" and that powerful countries will negotiate with them.

The U.N. nuclear chief said that the international community needs to make sure that THAT is not the lesson that people would learn from North Korea.

ElBaradei spoke during a question-and-answer session at the Council on Foreign Relations in New York on Friday.