US intelligence agencies, including the FBI and the Pentagon, are investigating a leak of classified US intelligence related to Israel's plans for retaliatory strikes against Iran, according to a report by Axios.

The leaked documents, dated October 15 and 16, appeared on the messaging app Telegram via an account named "Middle East Spectator." Marked as top secret, the documents were intended for viewing only by the US and four of its closest allies: Australia, Canada, New Zealand, and the United Kingdom.

The leaked documents reveal sensitive details about Israel's plans for a potential strike on Iran, including the movement of munitions. One document, sourced from the National Security Agency (NSA), describes Israeli Air Force exercises involving air-to-surface missiles, believed to be in preparation for an attack on Iran. 

The leaked documents also suggest that Israel has nuclear weapons capabilities—something the country has never publicly confirmed—although the documents do not indicate that Israel would deploy such weapons.

Following the leak, a US official confirmed that federal agencies are investigating who had access to the classified Pentagon materials. According to CNN, such a leak automatically triggers an inquiry by the FBI, Pentagon, and US intelligence agencies.

The leak comes at a tense time, as Israel has been preparing for retaliatory action against Iran following a missile attack by Iran on October 1. Israeli officials are likely to be frustrated by the breach, especially given their recent disagreements with the US over its handling of ongoing regional conflicts in the Middle East.

“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,” said former deputy assistant secretary of defense for the Middle East Mick Mulroy, according to CNN.

“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,” Mulroy added.

House Speaker Mike Johnson also addressed the leak, calling it "concerning" and stating that he is closely monitoring the situation.

“The leak is very concerning. There’s some serious allegations being made there, an investigation underway, and I’ll get a briefing on that in a couple of hours,” Johnson told CNN's Jake Tapper. “We’re following it closely.”

Johnson added that he had spoken with Israeli Prime Minister Benjamin Netanyahu to offer his support, emphasizing that the US must stand firmly by its ally. 

“I think that the United States needs to stand unequivocally by our ally there… we’re on a precipice… of a new era of security and freedom for Israel. And I think we’re very close,” said Johnson.