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Iran explored 'fourth-generation' nuclear weapon - report

Dec 19, 2025, 10:53 GMT+0
Pigeons fly on street in Tehran, Iran, November 22, 2025.
Pigeons fly on street in Tehran, Iran, November 22, 2025.

Iran explored advanced nuclear weapon concepts based on pure fusion before its war with Israel, an Israeli media report said, describing research into a theoretical approach that does not require uranium or plutonium.

The report, published by Yedioth Ahronoth on Friday, said Iranian scientists examined what it described as a “fourth-generation” nuclear weapon based on pure fusion, a technology that no country is known to have successfully produced.

“Such fusion does not require uranium or plutonium, and produces almost no radiation or fallout,” the report said.

Why pursue fusion research

The Israeli report said it was unclear why Iran pursued research into pure fusion given the extreme technical difficulty of the approach.

It outlined several possible explanations, including that the work was meant to obscure continued interest in conventional nuclear weapons, to explore ways around international non-proliferation frameworks, or to build scientific knowledge that could shorten development timelines if Tehran later chose another path.

Another explanation cited was that Iran sought experience with highly complex nuclear physics challenges, even if the fusion route itself was not practical.

Washington Post cites intelligence from 2023

The Israeli account broadly aligns with reporting this week by the Washington Post, which said US and Israeli intelligence agencies began gathering information in 2023 indicating that Iranian scientists were exploring several nuclear weapon paths, including fusion-based concepts.

The Post said US intelligence assessed that Iranian researchers were also studying a crude fission device that could be built more quickly if Iran’s leadership reversed a long-standing ban on nuclear weapons, while fusion research was viewed as more aspirational.

US and Israeli analysts agreed that a fusion weapon would be “beyond Iran’s reach,” the Post said.

Satellite images show site activity

Separately, a US-based think tank said satellite imagery shows new activity at Iran’s Natanz nuclear site, which was damaged during the June conflict.

The Institute for Science and International Security said images taken in December show Iran placing panels over a destroyed enrichment facility at Natanz.

“Satellite imagery from December shows Iran placed panels on top of the remaining structure, providing cover for the destroyed facility,” the think tank said.

Iran says its nuclear program is peaceful, while Western governments and Israel say Iran’s nuclear activities raise proliferation concerns.

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