A fire ripped through a building at Iran’s main nuclear-fuel production site early Thursday, causing extensive damage to what appeared to be a factory where the country has boasted of producing a new generation of centrifuges. The United States has repeatedly warned that such machinery could speed Tehran’s path to building nuclear weapons.

The Atomic Energy Agency of Iran acknowledged an “incident” at the desert site, but did not term it sabotage. It released a photograph showing what seemed to be destruction from a major explosion that ripped doors from their hinges and caused the roof to collapse. Parts of the building, which was recently inaugurated, were blackened by fire.

But it was not clear how much damage was done underground, where video released by the Iranian government last year suggested most of the assembly work is conducted on next-generation centrifuges — the machines that purify uranium.

A Middle Eastern intelligence official, who spoke on the condition of anonymity to discuss closely held information, said the blast was caused by an explosive device planted inside the facility. The explosion, he said, destroyed much of the aboveground parts of the facility where new centrifuges — delicate devices that spin at supersonic speeds — are balanced before they are put into operation.

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