Hours after it reported an “accident” at its Natanz nuclear complex, and said there were no casualties or radioactive pollution, Iran on Thursday warned that it would weigh its response to “hostile countries,” including Israel and the US, if they had crossed Iran’s “red lines in any way.”

The New York Times quoted an unnamed Middle Eastern intelligence official saying an explosion had taken place as the result of a bomb planted inside the facility.

The source was quoted as saying that the blast had destroyed the above-ground areas of the facility, which he said houses centrifuges.

Iran initially downplayed Thursday morning’s events at Natanz, initially claiming vaguely there had been an unspecified “incident” and later acknowledging a fire.

Later it elaborated on what it still called an accident, and issued assurances that there was no danger of radioactive fallout, but it subsequently also issued a warning to its foes.

US-based analysts said the building, located above Iran’s underground Natanz enrichment facility, was a new centrifuge production plant and that it was hit by a fire and an explosion.

Asked about reports of the incident at a press conference Thursday evening, Israel’s Prime Minister Benjamin Netanyahu brushed aside the question: “I don’t address these issues,” he said.

The site of the fire corresponds to a newly opened centrifuge production facility, said Fabian Hinz, a researcher at the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies in Monterey, California. He said he relied on satellite images and a state TV program on the facility to locate the building, which sits in Natanz’s northwest corner.

David Albright of the Institute for Science and International Security similarly said the fire struck the production facility. His institute previously wrote a report on the new plant, identifying it from satellite pictures while it was under construction and later built.

There was “no nuclear material [at the building] and no potential of pollution,” the spokesman for Iran’s Atomic Energy Organization Behrouz Kamalvandi told state television. Kamalvandi said no radioactive material or personnel were present.

He noted that the cause was being investigated, and said the fire had led to “some structural damage.”

There was “no interruption to the work of the enrichment site itself,” which “is working at the pace it used to,” Kamalvandi said.

Harbingers Daily Note – Amir Tsarfati, founder and president of Behold Israel, commented on the explosion today at Natanz Nuclear Facility, saying that it appears to be a series of “inside jobs sponsored by an enemy country”. Tsarfati referencing two additional explosions in Iran within the span of a week, with Thursdays being the third such incident.

Hours after the announcement, Iran’s state news agency IRNA published an editorial warning that “if there are signs of hostile countries crossing Iran’s red lines in any way, especially the Zionist regime (Israel) and the United States, Iran’s strategy to confront the new situation must be fundamentally reconsidered.”

IRNA also reported that unnamed Israeli social media accounts had claimed the Jewish state was responsible for the “sabotage attempts.”

An unnamed former Iranian nuclear official told Reuters that sabotage was a possibility. “Considering that this so-called incident happened just a few days after the explosion near the Parchin military base, the possibility of a sabotage cannot be ruled out,” this source said. “Also Natanz enrichment facility has been targeted in the past by a computer virus,” he added, referring to Stuxnet.

The incident came six days after an explosion near a military complex rocked the Iranian capital.

The blast in the Parchin area in the southeast of Tehran was due to “leaking gas tanks,” Iran’s defense ministry said on Friday.

Parchin is suspected of having hosted conventional explosion tests with nuclear applications, which the Islamic republic denies.

The explosion near Parchin, which rattled Iran’s capital on Friday, came from an area in its eastern mountains that analysts believe hides an underground tunnel system and missile production sites, based on satellite photographs.