Supreme Leader Ayatollah Ali Khamenei addresses in a televised speech marking the annual Quds, or Jerusalem Day, in Tehran, Iran
Iran's Supreme National Security Council (SNSC) said that the country's experts have determined the main cause of a recent "incident" at the Natanz nuclear facility and will announce it at an "appropriate time".
Experts from different sectors started investigating "different hypotheses" about the "incident" at the Natanz site in central Iran immediately after its occurrence on Thursday, and have determined its main cause, SNSC spokesman Keyvan Khosravi was quoted as saying on Friday by Xinhua news agency.
"Due to some security considerations, the cause and manner of this incident will be announced at a proper time," said Khosravi.
The damage to one of the sheds under construction at the Natanz complex was "limited" and investigators did not find any nuclear material at the building, he said.
The Iranian security official emphasised that there has been no radioactive contamination following the "incident".
On Thursday, Ramazan Ali Ferdowsi, governor of Natanz County said that the fire at Iran's Natanz nuclear facility caused no damage to the establishment.
The blaze affected one of the structures for storing stock items and was contained by the firefighters, Ferdowsi said.
"Nobody has been hurt and the regular activities of the facility have not been affected," Behrouz Kamalvandi, spokesman for Atomic Energy Organisation of Iran, was also quoted as saying by official IRNA news agency on Thursday.
Kamalvandi confirmed that only one of the structures under construction was damaged.
There were no concerns about pollution as the fire took place in an inactive area of the establishment, he said.
The facility is a Fuel Enrichment Plant covering 100,000 square meters.
It is located in Natanz, the capital city of Isfahan province.