The Pentagon considered Monday that the likely leak of classified US documents related to the Russian invasion of Ukraine , most of which appear to be original documents, poses a "very serious" threat to the national security of the United States.

Here's what we know about the anonymous leak, which only recently caught the media's attention.

Many of these documents are related to the war in Ukraine. Some of them assess the situation of the conflict at the beginning of March, including the size of the Russian and Ukrainian losses, while others address the situation on specific fronts, such as Bakhmut.

The documents talk, among other topics, about Kiev's air defenses, which are crucial to countering Russian strikes, and about international assistance to Ukrainian forces.

Some of these documents also seem to indicate that the United States is spying on some of its allies: one of these documents says that leaders in the Israeli intelligence service "Mossad" are defending the demonstrations against the controversial reform of the judicial system in the Jewish state.

And on Sunday, the US Department of Defense (The Pentagon) said that it was working to “evaluate the authenticity of the video documents circulating on social networks,” but admitted that they “apparently contain very sensitive and confidential information.”

And press reports quoted US officials that most of these documents are original, but it seems that at least one of them was forged to indicate that Ukraine's losses exceeded Russia's losses, while the document, which is supposed to be original, confirms the opposite.

The US Department of Justice has opened a criminal investigation as the Department of Defense evaluates the potential national security consequences of this leak.

The Pentagon said that US officials have contacted Washington's allies about this matter, and the relevant parliamentary committees have been briefed.

US Defense Department spokesman Chris Meagher told reporters on Monday that the circulation of these documents on the Internet poses "a very serious threat to the national security of the United States and that they may spread misleading information."

The leak could jeopardize US intelligence sources, as well as provide Russia with valuable information on the conditions of Ukrainian forces.

Documents dealing with partner countries of the United States could be an embarrassment to Washington, especially those that refer to possible US espionage operations on close allies.

Dozens of documents and images have been leaked on Twitter, Telegram, Discord and other sites in recent days, but many of them are no longer available on these sites, as it appears that the United States is working to remove them.

The investigative website Bellingcat said that some of these documents have been circulating on the Internet since before January 2023.