Iran is on the threshold of nuclear capability and has mastered critical steps needed to build a weapon after receiving assistance from a foreign scientist, a media report said. The country has overcome key technical hurdles with the help of a former Soviet weapon scientist and crucial technology linked to experts in Pakistan and North Korea, The Washington Post reported quoting Western diplomats. The diplomats and nuclear experts briefed on the findings by UN officials said a rouge Soviet scientist had tutored Iranians over several years on building high-precision detonators for the weapons. The intelligence update would be circulated among members of the International Atomic Energy Agency (IAEA) this week and is expected to focus on Iran’s alleged efforts towards putting radioactive material in a warhead and developing missiles. The key breakthrough in Iran’s quest for nuclear weapons was its success in obtaining design information for a device known as R265 generator. Citing diplomats, the Post said the key breakthrough was provided by Vyacheslav Danilenko, a former Soviet nuclear scientist who was contracted in the mid-1990s by Iran’s Physics Research Centre. 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. Danilenko’s role was judged to be so critical that IAEA investigators devoted considerable effort to obtaining his cooperation, the two officials said. There is no evidence that the Russian government knew of Danilenko’s activities. Iran relied on foreign experts to supply formulas and codes for theoretical design work, some of which appear to have originated in North Korea. Additional help appears to have come from the father of Pakistan’s nuclear programme, Abdul Qadeer Khan, whose design for a device known as a neutron initiator was found in Iran, sources said. Meanwhile, the US said Monday the Iran’s nuclear weapons programme was a matter of “serious concern” and it was in consultation with Israel on the issue amid reports the Jewish state might consider unilateral strike against Iranian atomic facilities. “Iran’s nuclear weapons remains a serious concern to the US and to Israel,” George Little, the Pentagon Press Secretary said. “The (Defence) Secretary believes we have a strong military relationship with Israel,” he said.