The United States has launched an urgent investigation into the leaking of classified documents describing an American assessment of Israel's plans to attack Iran.

The top secret files are said to describe satellite imagery showing Israel moving military assets in preparation for a response to Iran's ballistic missile attack back on 1 October.

It has separately also been reported that the UK may tacitly support the move to strike back against Iran in a measured fashion, though no official such backing has been made public by the government.

Instead, Britain has so far stuck to the line that Israel has the right to defend itself.

But UK forces were involved in supporting Israel after Iran launched the ballistic missile attack on the country, the defence secretary John Healey later revealed.

Meanwhile, the leaking of the top secret documents is an embarrassment to the White House.

The files were reportedly published online last week and House of Representatives Speaker Mike Johnson yesterday confirmed that a probe into how this happened has now been launched.

The documents, marked top secret, were shareable within the Five Eyes intelligence alliance of the US, Britain, Canada, New Zealand and Australia, according to American broadcaster CBS.

Two of them appeared to be attributed to the US National Geospatial Intelligence Agency and National Security Agency (NSA), and were published on an Iranian-aligned Telegram account on Friday.

One of the files made a reference to Israel’s nuclear capabilities - which neither the US nor Israel ever officially acknowledge - apparently ruling out the use of such an option in any planned strike.

But Mr Johnson, the highest-ranking member of Congress, admitted that "the leak is very concerning".

"There's some serious allegations being made, there's an investigation under way, and I'll get a briefing on that in a couple of hours," the Louisiana Republican lawmaker said.

The Pentagon confirmed in a statement that it was aware of reports about the documents, but did not comment further.

The US agencies involved, as well as the Israeli government, have not publicly commented on the leak.

One former American intelligence official said the unauthorised release was probably an attempt to expose the scale of the planned retaliation, possibly to disrupt it.

The US is investigating whether the information was intentionally leaked by an American agent, or whether it was stolen, possibly through hacking, officials explained.

The two documents appear to be based on satellite information obtained from 15-16 October.

The first is titled: "Israel: Air Force Continues Preparations for Strike on Iran and Conducts a Second Large-Force Employment Exercise," according to Reuters news agency. It describes ballistic and air-to-surface missile handling.

The second is titled: "Israel: Defense Forces Continue Key Munitions Preparations and Covert UAV Activity Almost Certainly for a Strike on Iran". It discusses Israeli drone movements.

For weeks Israel has been deciding how and when to respond to Iran's latest missile attack. Israel's defence minister has warned it will be “deadly, precise and surprising”.

US President Joe Biden said last week that he had a "good understanding" of what Israel was planning.

"Do you have a good understanding of what Israel is going to do right now in response to Iran... and when they will actually respond?" a reporter asked him.

"Yes, and yes," Mr Biden replied.

Meanwhile, Israel yesterday again launched multiple strikes across Lebanon targeting banks, hitting the capital Beirut again.

As the death toll from an attack on Gaza on Sunday reached 87, the Israeli military claimed its operation in Lebanon was now focusing on Hezbollah’s ‘financial infrastructure’ as it issued further evacuation orders amid renewed air strikes.

The Israeli military issued 24 warnings of air strikes in less than an hour, with evacuation warnings causing widespread panic, according to the UN's envoy to Lebanon.

The Al-Qard al-Hassan bank has been under US sanctions since 2007, with the US saying it allows Hezbollah to bypass banking systems.

Two strikes were reported close to Beirut airport, as passenger planes were still landing.

After the latest attacks on the capital Beirut, Israel's Foreign Minister Israel Katz said they constituted a "wide-scale Israeli attack" which "targeted Hezbollah's financial infrastructure".

He added: “Beirut in flames. Massive fires were seen above Beirut as over 15 buildings were struck following evacuation warnings to residents.

"Hezbollah has paid and will continue to pay a heavy price for its attacks on northern Israel and its rocket fire.
"We will keep striking the Iranian proxy until it collapses."