TEHRAN (Reuters) - Iran has developed a version of the Russian S-300 missile and will test-fire it soon, the official news agency IRNA said, two months after Moscow decided not to deliver it to Tehran to comply with UN sanctions. The Iranian (version) of the S-300 system is undergoing field modification and will be test-fired soon as other long range systems are being designed and produced, IRNA quoted Brigadier General Mohammad Hassan Mansourian, a commander in Irans elite Revolutionary Guards, as saying. World powers are locked in an eight-year-old stand-off with Iran over its nuclear energy programme, which they believe will be used to develop nuclear bombs rather than be devoted to peaceful generation of electricity, as Tehran says. Some Western officials suspect Irans development of more sophisticated missiles and some much-publicized missile tests could serve the goal of developing a deliverable nuclear weapon. The Islamic Republic denies such accusations, saying its missile development efforts are for defensive purposes only. Russian President Dmitry Medvedev banned the delivery of the high-precision S-300 air defence system to Iran in September, scuttling a tentative deal in gestation for years, saying it would violate expanded UN sanctions imposed in June over Irans defiance of demands to curb its nuclear programme. Iranian officials said after Russia scrapped the sale that Tehran had decided to build its own model of the S-300 but gave no sign that such plans had advanced beyond the drawing board. Buying S-300 missiles from the Russia was on the agenda to meet some of the security needs of our country, said Mansourian. But under the pretext of the (UN Security Council) resolution and due to American and Zionist pressure, Russia refused to deliver the defensive system. The Revolutionary Guards oversee Irans missile programme. The United States and Israel had urged Moscow to scrap the deal, fearing Iran could use S-300s to shield nuclear facilities that they suspect are part of an atomic bomb programme. US and Israeli officials have not ruled out a pre-emptive attack to knock out Irans nuclear sites if diplomacy fails. Iran this week offered world powers some dates for renewed talks but President Mahmoud Ahmadinejad said on Thursday the disputed nuclear programme would not be up for negotiation. The Islamic Republic has warned that its response to any military attack would be crushing. Iranian officials have criticized their Russian counterparts for unilaterally nullifying the S-300 sale contract and threatened to seek compensation.