Iran has arrested some of those responsible for assassinations of its nuclear scientists, state media reported on Sunday, in a continued hunt for those it says are working to sabotage its nuclear program.Intelligence minister Heydar Moslehi said Iran had shut down two networks inside and outside the country he said were involved in training the killers, Fars News Agency reported.At least four scientists associated with Iran's nuclear disputed nuclear works have been slain since 2010 and a fifth - Fereydoun Abbasi Davani, now the head of Iran's Atomic Energy Organization - was wounded.The West believes Iran is stockpiling enriched uranium as potential fuel for nuclear weapons and trying to develop technology needed for a workable bomb. Iran denies this, saying its nuclear activity is solely for peaceful energy purposes.Moslehi did not say how many people had been arrested, for which killings they were allegedly responsible, where the networks were operating or how they trained the assassins."They [the two networks] took steps not to leave any clues behind but they were stricken by mistakes," he said.Moslehi spoke at a ceremony marking the first anniversary of the shooting death of Dariush Rezainejad. Initial reports in Iranian media suggested Rezainejad was involved in Iran's nuclear program, but later said he was an engineering student."We were able to arrest the main actors in this act of terrorism," Moslehi was quoted as saying.Iran blames the assassinations on US, Israeli, French, British and German spy agencies, especially the Mossad. In May, Iran hanged 24-year-old Jamal Fashi for the murder of scientist Massoud Ali-Mohammadi in January 2010, saying that Fashi had gone to Israel for training.“After reconstructing the assassination scene we are certain that the detainees have been involved in the assassination and carried out their measure with the support of the CIA and Mossad,” Moslehi said on Sunday, according to semi-official Iranian news agency Press TV.The United States has denied any role in the killings. Israel has remained silent.Sporadic talks between six world powers and Iran to defuse the decade-long stand-off over its nuclear ambitions have so far failed to yield a breakthrough.A European Union ban on the import, purchase or shipping of Iranian oil took effect on July 1 as part of widening international sanctions aimed at prodding Tehran into curbing enrichment and opening up to UN nuclear inspections.