It had all the trappings of sabotage: an explosion at a major nuclear facility in Iran, allegedly confirmed by an Israeli official. But it all turned out to be speculation, the White House said on Monday, debunking the sensational story.

An Iranian exile who goes by the name of Reza Kahlili reported the alleged blast in Fordow four days ago on World News Daily, a far-right website known for publishing conspiracy theories about President Obama’s birthplace.

The report was initially ignored by mainstream news sites but got more traction on Monday when London’s Times cited an Israeli official confirming the explosion. Other news organizations then picked up on the story, sourcing it back to The Times.

But White House spokesman Jay Carney, responding to questions about the report at a briefing Monday, said that Washington didn’t believe it. “We have no information to confirm the allegations in that report, and we do not believe the report is credible.”

The confusion underscored one of the challenges of reporting on the shadow war Israel and the United States are apparently waging against Iran’s nuclear program. Both countries are believed to be involved in acts of sabotage inside the country—and much of Iran’s nuclear enrichment takes place at Fordow.

Kahlili, who published more details on WND on Tuesday, is a frequent commentator on Iran. In a book he published last year, he described having spied for the CIA in the ’80s and ’90s while serving in Iran’s Revolutionary Guards. Kahlili is a pseudonym.

In a phone interview with The Daily Beast on Monday, Kahlili said his sources for the report came from inside Iran’s security establishment. He said Iran pays lobbyists in Washington to discredit reports by Iranian exiles and tarnish their image.

“Anyone who takes up this struggle against the regime is labeled a neo-con and a war monger,” he said. “I don’t have an agenda except freedom for Iran. This regime is a danger to Iranians and the world.”

But experts said distinguishing between credible and noncredible sources among Iranian exiles—not just for journalists but for intelligence agencies as well—can be a tricky business.

Ephraim Kam, a retired colonel in Israel’s military intelligence and the deputy director of the Institute for National Security Studies in Tel Aviv, said he had doubts about the story all along.

“The fact that the Iranians deny it doesn’t mean much. They will always deny it,” Kam told The Daily Beast.

“But there was just one source and I’m not sure he’s reliable enough. And usually, you would expect something to be visible on the surface, maybe photos of a fire or evidence of rescue operations. That didn’t exist here.”

Kam also said remarks by Israeli officials, including Strategic Affairs’ Moshe Yaalon, seemed to suggest an uncertainty in the security establishment about whether the explosion actually took place.

Yaalon told Army Radio that he learned about the Fordow incident from a newspaper. He said every act of sabotage could potentially slow Iran’s progress toward nuclear weapons but had no specific comments about the report.

Meir Javedanfar, a frequently cited Israeli commentator on Iran, had a similar assessment.

“It could be true or it could be nothing more than a figment of someone’s imagination,” Javedanfar wrote on his website Sunday. “When it comes to this type of report, you need to have at least two credible sources, if not more.”

Iran has accused Israel and the United States of planting viruses in the computers of its nuclear installations and assassinating its atomic scientists. The regime claims its nuclear program is for peaceful purposes.