The United States is investigating the leak of a pair of highly classified intelligence documents describing Israel's preparations for a retaliatory strike on Iran, House Speaker Mike Johnson said on Sunday.

The documents appear to have been prepared by the National Geospatial-Intelligence Agency, describing U.S. interpretations of Israeli Air Force and Navy planning based on satellite imagery from Oct. 15-16. They began circulating last week on the Telegram messaging app.

Israel has been planning a response to a ballistic-missile barrage carried out by Iran on Oct. 1, its second direct attack on Israel in six months. Israel has intensified its offensive in Gaza and Lebanon, days after the killing of Hamas leader Yahya Sinwar.

Asked about the leak of the documents during an interview with CNN, Johnson, the U.S. House of Representatives' top lawmaker, said an "investigation (is) underway and I'll get a briefing on that in a couple of hours."

."..We are following it closely," Johnson added.

The National Geospatial-Intelligence Agency and the Office of the Director of National Intelligence did not immediately respond to requests for comment. The Pentagon said it was looking into the leak reports.

The New York Times reported that officials acknowledged privately that the documents were authentic, but that they likely only represent a portion of information the U.S. has on its close ally's planning.

The first document is titled: "Israel: Air Force Continues Preparations for Strike on Iran and Conducts a Second Large-Force Employment Exercise." It describes activities including 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." UAVs are also known as drones. U.S. President Joe Biden, responding to questions from reporters, said last week he had a good understanding of when and how Israel would attack Iran. But he also said he sees an opportunity to end the two enemies' back-and-forth strikes.