The US is conducting an investigation into a leak of highly classified intelligence that reveals Israel's plans for a potential retaliatory strike against Iran, according to three individuals familiar with the situation, CNN reported.
One of these sources has confirmed the documents' authenticity.
A US official described the leak as "deeply concerning", the American news outlet reported.
The documents, dated October 15 and 16, began circulating online on Friday after being posted by an account named "Middle East Spectator" on Telegram. They are marked as top secret and are intended for only the US and its "Five Eyes" intelligence-sharing partners: Australia, Canada, New Zealand, and the United Kingdom.
These documents outline Israel's apparent preparations for a military strike against Iran.
One document, sourced from the National Geospatial-Intelligence Agency, details Israel moving munitions as part of these preparations.
Another document, attributed to the National Security Agency, describes Israeli air force exercises involving air-to-surface missiles, which are believed to be in preparation for the strike.
A US official indicated that the investigation is focused on identifying who had access to the sensitive Pentagon material.
Such a leak automatically prompts a joint investigation by the FBI, the Pentagon, and US intelligence agencies.
The FBI has declined to comment on the situation, reported CNN.
The leak occurs at a particularly delicate time in US-Israel relations and is likely to infuriate Israel, which has been preparing to retaliate against Iran following a missile barrage on October 1.
One document also suggests something Israel has never publicly confirmed: the existence of its nuclear weapons.
The document, however, notes that the US has seen no evidence that Israel plans to use nuclear weapons against Iran.
Mick Mulroy, former deputy assistant secretary of defence for West Asia and a retired CIA officer said, "If it is true that Israeli tactical plans to respond to Iran's attack on October 1 have been leaked, it is a serious breach."
He added, "The future coordination between the US and Israel could be challenged as well. Trust is a key component in the relationship, and depending on how this was leaked that trust could be eroded."
Another US official noted, "These two documents are bad, but not horrible. The concern is if there are more."
It remains unclear how the documents were leaked, whether they were hacked or deliberately made public.
The US has been on heightened alert regarding Iranian cyber campaigns, with US intelligence agencies in August reporting that Iran had hacked documents belonging to Donald Trump's campaign, CNN reported.
The leak, first reported by Axios, comes after a major intelligence breach last year, when a 21-year-old Air National Guardsman posted highly classified information on Discord, damaging US relations with key allies, including South Korea and Ukraine.
