An Iranian flag, amid a ceasefire between U.S. and Iran, in Tehran, Iran, April 27, 2026. Majid Asgaripour/WANA (West Asia News Agency) via REUTERS Purchase Licensing Rights , opens new tab
VIENNA, May 29 (Reuters) – Iran and the United States are in discussions to extend their ceasefire so as to start negotiations on issues including Tehran’s nuclear program, where Washington insists Iran must not be able to make a nuclear weapon.
While much of Iran’s uranium enrichment infrastructure was destroyed or badly damaged when Israel and the U.S. bombed it in June, a large part of the highly enriched uranium it amassed is thought to have survived. That is the biggest U.S. concern ahead of nuclear talks.
On Friday Trump said in a social media post that Iran must agree that the enriched uranium buried underground after earlier U.S. strikes be “unearthed” and destroyed in coordination with Iran and the U.N. nuclear watchdog.
WHAT IS HIGHLY ENRICHED URANIUM?
One of two fissile materials, along with plutonium, with which one can make the core of a nuclear bomb.
While plutonium is usually extracted from the spent fuel of a nuclear reactor, requiring large and highly visible infrastructure, uranium can be enriched using centrifuges that have a much smaller footprint.
Two of Iran’s three enrichment sites that are known to have been operating when Israel and the U.S. attacked in June were underground. The above-ground one was clearly destroyed.
Uranium is highly enriched when it has reached 20% purity, and weapons-grade as of around 90%.
Modern reactors generally use fuel enriched to up to 5%, but some use fuel enriched to higher levels. The ones that power U.S. nuclear submarines reportedly use fuel enriched beyond 90%.
HOW MUCH DOES IRAN HAVE?
Iran has not informed the U.N. nuclear watchdog of the fate of its enriched uranium since the June attacks or let its inspectors return to the sites where it was stored.