Iran claims to have smuggled almost all of the country’s highly enriched uranium to a secret location before the US launched strikes on its nuclear bases.

Three of Tehran’s most critical enrichment facilities, including its underground facility at Fordow, were pummelled by B-2 stealth bombers and a barrage of submarine-launched missiles early on Sunday morning.

But officials believe that most of the material at Fordow and Iran’s other facilities had been moved elsewhere before the strikes.

Iran has vowed to continue enriching uranium in defiance of Donald Trump, raising further concerns over its nuclear programme.

Takht Ravanchi, Iran’s deputy foreign minister, rejected claims that Tehran would abandon its nuclear programme, telling the Germany broadcaster ARD: “No one can tell us what we should and should not do.”

Following the mission, codenamed Midnight Hammer, the US president claimed to have “obliterated” Iran’s nuclear aspirations in the wave of strikes. He said the US had taken the bomb “right out of Iran’s hands” by inflicting “monumental damage” on the Fordow, Natanz and Isfahan facilities.

However, doubt has been cast on Mr Trump’s claims after senior US officials admitted they did not know the fate of Iran’s near-bomb-grade uranium stockpile.

Rafael Grossi, the head of the International Atomic Energy Agency (IAEA), said on Monday that extensive damage was expected to have occurred at the Fordow, but added that his agency was seeking access to “account for” Iran’s highly enriched uranium stockpiles.

Two Israeli officials with knowledge of the intelligence told The New York Times that Iran had transferred equipment and uranium outside Fordow in recent days.

There was also evidence to suggest Iran had moved its 400kg stockpile of 60 per cent enriched uranium, which had been stored inside Isfahan, to a secret location.

JD Vance, the US vice president, hinted that the material had been moved at the 11th hour on Sunday. “We’re going to work in the coming weeks to ensure that we do something with that fuel,” he told ABC News.

Mr Grossi said the fuel had last been seen by UN inspectors a week before Israel began its attacks on Iran on June 13.

According to satellite imagery, trucks, bulldozers and security convoys appeared to swarm the Fordow facility two days before the US strikes. Analysts at TS2 Space, a Polish defence firm, suggested it revealed a “frantic effort” to move centrifuges or shielding materials.

Initial assessments suggest the fortified site at Fordow had sustained serious damage from the Massive Ordnance Penetrator (Mop) bombs, but had not been completely destroyed. Satellite images suggested that the bombs had a severe impact.

The already-damaged facility at Isfahan was hit by dozens of missiles, but it contained little or no enriched uranium when it was hit, the IAEA said.

Other images showed that Natanz, Iran’s largest enrichment site, had already been damaged by extensive Israeli strikes, which disrupted the electrical system. Mr Grossi later said he believed the loss of power at Natanz could have sent the centrifuges spinning out of control, likely to have destroyed all of them.

Moving its stockpile to a secret location means Iran could still possess the material needed to develop a nuclear weapon, depending on Tehran’s ability to rebuild vital equipment, including centrifuges, which could take years.

Ronen Solomon, an Israeli intelligence analyst, told The Telegraph that even if Iran had moved its uranium, it would be “like having fuel without a car”, adding: “They have the uranium, but they can’t do a lot with it, unless they have built something we don’t know about on a small scale.”

Ali Shamkhani, an adviser to the supreme leader, said: “Even assuming the complete destruction of the sites, the game is not over, because enriched materials, indigenous knowledge, and political will remain intact.”

Uranium enrichment is the process of increasing the concentration of the uranium-235 isotope in natural uranium. To build a nuclear weapon, uranium must be enriched to about 90 per cent U-235.

Iran enriches uranium using centrifuges, which spin uranium hexafluoride gas at high speeds to separate the uranium isotopes, increasing the concentration of U-235.

It has been progressively installing more advanced centrifuges, like the IR-2m and IR-6 models, which are faster and more efficient than the older IR-1 centrifuges, speeding up the time needed to make a nuclear bomb.

Iran’s centrifuge capacity before the Israeli and US strikes could have allowed it to produce enough weapons-grade uranium for a bomb in less than two weeks, according to the Arms Control Association.

It is transported inside steel cylinders, specially designed to withstand significant pressure and temperature changes, according to the World Nuclear Association. The cylinders are then placed inside an extra level of protective casing, called an overpack, and can be transported via rail, road and sea.

Iran produces most of its near weapons-grade material at Fordow. As of May 17, Iran had amassed 408.6kg (901lb) of uranium enriched up to 60 per cent, a report by the IAEA found. It was an increase of 133.8kg from the IAEA’s last report in February. (Yahoo news)