Leaders in six countries without nuclear weapons have openly discussed developing their own, as the head of the UN's atomic agency warns the world is at risk of a fresh nuclear arms race. Rafael Grossi , the director general of the International Atomic Energy Agency , expressed concern that some of the 191 signatories of the 1970 Nuclear Non-Proliferation Treaty (NPT) could begin breaching the pact, potentially triggering a "domino" effect in which as many as 20 states could pursue a bomb.