Iran will not stop higher-grade enrichment of uranium in response to external demands, Tehran’s top nuclear official was quoted as saying on Tuesday, signaling a tough bargaining stance ahead of planned new talks with world powers.Western powers want Iran to halt enrichment of uranium to a fissile concentration of 20 percent as it represents a significant step closer to the level that would be required to make nuclear bombs. Iran says it needs uranium refined to 20 percent to run its medical research reactor in Tehran."The Islamic Republic of Iran will not suspend 20 percent uranium enrichment because of the demands of others,” said Fereydoun Abbasi-Davani, head of the Atomic Energy Organisation of Iran, according to the Iranian Students’ News Agency (ISNA). "The Islamic Republic of Iran will produce 20 percent enriched uranium to meet its needs and for however long it is required.”He did not specify what he meant by Iran’s needs. Western diplomats say Iran already has produced sufficient quantities to fuel its Tehran Research Reactor for several years. Abbasi-Davani has in the past said Iran plans to build another research reactor. "Twenty percent enrichment is the right of the Iranian nation for use in the Tehran reactor and it will defend this right with authority,” Abbasi-Davani said.His comments renewed Iranian defiance in negotiations with world powers that are expected to resume soon, aimed at finding a peaceful solution to the decade-old dispute over Tehran’s nuclear ambitions. But he did not appear to categorically rule out that Tehran at some point could shelve the activity.