A secret cable obtained by Al Jazeera's Investigative Unit reveals that Mossad sent a top-secret cable to South Africa on October 22, 2012, that laid out a "bottom line" assessment of Iran's nuclear work.
It appears to contradict the picture painted by Benjamin Netanyahu of Tehran racing towards acquisition of a nuclear bomb.
Writing that Iran had not begun the work needed to build any kind of nuclear weapon, the Mossad cable said the Islamic Republic's scientists are "working to close gaps in areas that appear legitimate such as enrichment reactors".
Such activities, however, "will reduce the time required to produce weapons from the time the instruction is actually given".
That view tracks with the 2012 US National Intelligence estimate, which found no evidence that Iran had thus far taken a decision to use its nuclear infrastructure to build a weapon, or that it had revived efforts to research warhead design that the US said had been shelved in 2003.
Netanyahu plans to address the US Congress on March 3 and warn against the nuclear compromise currently being negotiated between Tehran and world powers.
Media reports and public comments by senior current and former officials have frequently indicated dissent from within Israel's security services over Netanyahu's alarmist messaging on Iran.
However, the document leaked to Al Jazeera makes clear that the Mossad's formal assessment of Iran's nuclear capacity and intentions differs from the scenario outlined by the prime minister at the UN.
The cable was relayed to South Africa's State Security Agency (SSA) shortly after the September 2012 address in which Netanyahu had displayed a cartoonish diagram of a bomb with a fuse, marked with a 70 percent line and another "red line" at 90 percent.
The markers represented progress milestones in Iran's uranium enrichment work. He argued that medium-enriched uranium (which Iran had begun producing, saying it was needed to fuel a research reactor producing isotopes to fight cancer) took Iran 70 percent of the distance to enriching weapons-grade material.