The United Nations' International Atomic Energy Agency, the international body's nuclear watchdog, asked Iran to explain evidence suggesting that Iranian scientists have experimented with an advanced warhead design that may be used in nuclear weapons, according to a report in the British Guardian on Friday.
According to the report, the very existence of the technology, known as a "two-point implosion" device, is a military secret in both the United States and the United Kingdom, but according to an IAEA dossier unpublished until now, Iranian scientists may have tested high-explosive components of the design.
The paper quotes nuclear experts describing the discovery that Iran may have tested the design as a "breathtaking" development.
The Jerusalem Post could not confirm the Guardian report.
Technically, a two-point implosion consists of a chain of fusion-boosted fission weapons. The second stage is imploded by x-ray energy from the first stage. This radiation implosion is much more effective than the high-explosive implosion of the primary. Consequently, the secondary can be many times more powerful than the primary, without being bigger.
Thus, a two-point implosion device is particularly suited to being mounted on long-range ballistic missiles, the range and accuracy of which are in inverse ratio to the weight of the warheads mounted on them.
More stages could be added, theoretically creating a "multi-point implosion," but the result would be a multi-megaton weapon too powerful to be useful.
IAEA Director-General Mohamed ElBaradei is quoted by the paper as saying the evidence of Iranian weaponization "appears to have been derived from multiple sources over different periods of time, appears to be generally consistent, and is sufficiently comprehensive and detailed that it needs to be addressed by Iran".
The paper also quotes James Acton, a British nuclear weapons expert at the Carnegie Endowment for International Peace as saying: "It's remarkable that, before perfecting step one, they are going straight to step four or five ... to start with more sophisticated designs speaks of a level of technical ambition that is surprising."
A Western offer that aims to stymie Iran's nuclear ambitions would have most of its uranium shipped to Russia and France for processing, then returned to Iran. The deal would greatly limit Iran's ability to produce fissile material clandestinely.
The offer aims to assure that Iran's nuclear program indeed remains civilian, as the regime in Teheran insists.
Iran, however, has been delaying in giving a response.
Israel and the United States suspect the country's program is also military and that Teheran is attempting to procure nuclear weapons.