Iran hid the construction of its Natanz nuclear enrichment plant — until it was revealed by a dissident group — as well as its construction of centrifuges to enrich uranium, until inspectors acting on a tip found them behind a false wall in a Tehran clock factory.

Iran revealed a deep underground site in 2009 only when it became clear that the West had discovered it and was about to announce its existence.

Iranian officials have refused to answer questions about documents and computer files that suggest Iran has explored how to build a weapon and has researched explosive yields of different nuclear fuels.

While Mr. Abbasi’s comments seemed to confirm that some of the answers Iran had provided were false, it remained unclear what kind of abilities it was hiding or overstating.

Mr. Abbasi, who was the target of an assassination attempt two years ago in Tehran by what Iranian officials said were Israeli agents, said in a blunt speech at the I.A.E.A. meeting on Monday that the agency had been infiltrated by “terrorists and saboteurs.” He also disclosed two previously unreported bombings at Iran’s top uranium enrichment sites, suggesting that at least one may have been carried out based on information gained through compromised security within the I.A.E.A.

The news media in Israel, where the government of Prime Minister Benjamin Netanyahu has said it considered Iran its top threat and only months away from achieving atomic bombmaking capability, seized on Mr. Abbasi’s quoted remarks in Al Hayat and his speech, interpreting them as part of an Iranian strategy to further justify its rejection of I.A.E.A. inspection requests.

But one Israeli analyst, Uzi Eilam, former director of the Israel Atomic Energy Commission, said it was unclear why Iran would admit to having issued false information. It is particularly perplexing at this stage in what has been a long-running dispute that has escalated in recent months, as new Western sanctions have been imposed on Iran and as Israel has threatened a pre-emptive military strike on Iranian nuclear sites.