A senior Iranian official travelled to the North Korean capital Pyongyang during the second week of October to make the offer, the magazine quoted the sources as saying.
Diplomats and intelligence sources say Iran is pushing ahead with plans to enrich uranium in defiance of international pressure to stop developing sensitive nuclear technology to calm fears it is seeking nuclear weapons.
Iran’s Shahab-3 missiles are based on North Korea’s Nodong rockets and Pyongyang is Tehran’s most important partner in developing missile technology, Der Spiegel said.