The highly classified Pentagon documents which were leaked online in recent weeks, but which began being confirmed and reported as authentic by The New York Times and others only in the past few days, contain some embarrassing revelations. This has sent DOJ and US intelligence officials scrambling to discover the source of the leaks.

CNN is confirming Monday based on one of the documents which appeared online that the US has been spying on Ukrainian President Vladimir Zelensky - a disclosure which has caused officials in Kiev to be "deeply frustrated".

"One document reveals that the US has been spying on Zelensky," CNN reports. "That is unsurprising, said the source close to Zelensky, but Ukrainian officials are deeply frustrated about the leak."

The US intelligence document suggests that American officials have been worried about possible Zelensky decision-making to strike deep into Russian territory, which would escalate the war and potentially bring Russian and NATO into direct clashes:

The US intelligence report, which is sourced to signals intelligence, says that Zelensky in late February "suggested striking Russian deployment locations in Russia’s Rostov Oblast" using unmanned aerial vehicles, since Ukraine does not have long-range weapons capable of reaching that far.

An additional possibility is that the US intelligence community might be monitoring the Ukrainian presidency's office as part of efforts to oversee and account for how the tens of billions in aid sent to Kiev is being utilized. 

The Washington Post details that "many of the documents seem to have been prepared over the winter for Gen. Mark A. Milley, chairman of the Joint Chiefs of Staff, and other senior military officials, but they were available to other U.S. personnel and contract employees with the requisite security clearances."

Here are 14 more major revelations contained within the leaked intel document trove based on various media sources: 

Meanwhile, the expanding breadth of subject matter has many suggesting a US source is responsible. It's being called "a nightmare for the Five Eyes" - and could damage intelligence-sharing relationships between the US and its partner countries.

The breach could also prove embarrassing for Russia as it deals with the claims that US intelligence has deeply penetrated some key areas of government, such as the Defense Ministry.

"The focus now is on this being a U.S. leak, as many of the documents were only in U.S. hands," former Pentagon official Michael Mulroy told Reuters. As opposed to electronic downloads, it appears most or all of these leaks are in the form of photographs of paper documents.