The Iranian government has mastered the critical steps needed to build a nuclear weapon after receiving assistance from foreign scientists, The Washington Post reported. Citing unnamed Western diplomats and nuclear experts familiar with new intelligence to be released to the United Nations, the newspaper said a former Soviet weapons scientist had allegedly tutored Iranians on building high-precision detonators of the kind used to trigger a nuclear chain reaction. Crucial technology linked to experts in Pakistan and North Korea also helped propel Iran to the threshold of nuclear capability, the report said. An intelligence update will be circulated among International Atomic Energy Agency members on Tuesday or Wednesday. It is expected to focus on Iran's alleged efforts towards putting radioactive material in a warhead and developing missiles. Iranian officials have already seen the Vienna-based IAEA's information, diplomats told AFP, and Foreign Minister Ali Akbar Salehi said in comments published in Iran on Sunday that it was based on "counterfeit" claims. However Western officials said the intelligence reinforced concerns that Iran continued to conduct weapons-related research after 2003 when, according to US intelligence agencies, Iranian leaders halted such experiments in response to international and domestic pressures, The Post said. The paper noted that one key breakthrough that had not been publicly described was Iran’s success in obtaining design information for a device known as a R265 generator. The device is a hemispherical aluminum shell that is lined with pellets of high explosives and electrically wired so the detonations occur in split-second precision, the report said. The explosions compress a small sphere of enriched uranium or plutonium to trigger a nuclear chain reaction. Creating such a device is a formidable technical challenge, and Iran needed outside assistance in designing the generator and testing its performance, the paper said. According to the intelligence provided to the IAEA, key assistance in both areas was provided by Vyacheslav Danilenko, a former Soviet nuclear scientist who was contracted in the mid-1990s by Iran’s Physics Research Center, the paper said. Danilenko offered assistance to the Iranians over at least five years, giving lectures and sharing research papers on developing and testing an explosives package that the Iranians apparently incorporated into their warhead design, said The Post, citing two officials with access to the IAEA’s confidential files.