Iranian authorities upgraded the impact of a fire at the Natanz nuclear facility, now calling the damage “significant” after earlier downplaying it as “limited.” Iran says it isn’t yet clear what ignited the fire, which is one of several unusual events at the facility in recent weeks. The plant is considered Iran’s largest uranium enrichment facility and is located about 150 miles from Tehran. The New York Times reported that a Middle East intelligence official “with knowledge of the episode” said Israeli agents had placed a “powerful bomb” at the site, and that an Islamic Revolutionary Guards Corps member confirmed the blast. Atomic Energy Organization of Iran spokesman Behrouz Kamalvandi said Sunday that there were no human casualties in last week’s fire, but that “the financial losses were significant.” Earlier the governor of Natanz said the fire only damaged a building under construction and did not affect the main area of the facility.