The cause of a fire at Iran’s Natanz nuclear site is known, but will not be made public at this time due to “security reasons”, a security spokesman said.
The semi-official Tasnim news agency quoted spokesman Keyvan Khosravi of Iran’s Supreme National Security Council as giving the comment.
Mr Khosravi did not elaborate, but his comments show the concern felt at the highest levels in Iran over the incident early on Thursday.
US-based analysts have told The Associated Press the fire and apparent explosion at the site struck a new centrifuge assembly plant.
Iranian officials had sought to downplay the blast, saying it struck an under-construction “shed”.