At the beginning of April, the Group of Six (Germany, China, the US, France, Britain, and Russia) asked Iran to return to the negotiation table to discuss its nuclear programme, and the G8 countries reiterated the request in July, calling for Tehran to return to talks before September.

World leaders will again review Iran's nuclear programme during a G20 summit scheduled Sep 24-25 in Pittsburgh.

Experts believe that Iran will in the near future acquire the capacity to build a nuclear bomb and conduct a nuclear test similar to the one carried out by North Korea in May.

Tehran announced in late February that it had 6,000 operating centrifuges at its Natanz uranium enrichment facility.