TEHRAN, Iran (AP) — A spokesman says an “incident” has damaged an under-construction building near Iran’s Natanz nuclear site, but there was no damage to its centrifuge facility.

Behrouz Kamalvandi made the comment in a report published Thursday by the state-run IRNA news agency. Kamalvandi said authorities were investigating what happened.

He called the affected building an “industrial shed,” without elaborating. There hasn’t been any previously announced construction work at Natanz, a uranium enrichment center some 250 kilometers (155 miles) south of the capital, Tehran.

Natanz includes underground facilities buried under some 7.6 meters (25 feet) of concrete, which offer protection from airstrikes