The head of the UN nuclear watchdog Iran has failed to answer questions about the discovery of uranium particles at former undeclared sites in the country, calling on Tehran to provide information without further delay.Rafael Grossi, the head of the International Atomic Energy Agency, has been pushing Iran for answers on three sites dating back many years where inspections had revealed traces of uranium of man-made origin, suggesting they were once connected to Iran’s nuclear programme.Grossi is concerned that nuclear material has been present at the three undeclared locations in Iran and that the current locations of this nuclear material are not known by the agency.