The Pentagon said Monday that the leak likely of classified US documents related in particular to the Russian war on Ukraine, most of which appear to be original, poses a "very serious" risk to the national security of the United States.

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

  • What are these documents?

Many of these documents are related to the war in Ukraine. Some assess the situation of the conflict in early March, including the extent of Russian and Ukrainian casualties, while others address the situation on specific fronts, such as Bakhmut.

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

Some of these documents also appear to indicate that the United States is spying on some of its allies, one of which, for example, says that leaders in Israel's Mossad intelligence service are defending demonstrations against controversial reform of the justice system.

  • Is it real?

The Pentagon said it was working to "assess the authenticity of video documents circulating on social networks," but acknowledged that they "appear to contain very sensitive and classified information."

Press reports quoted U.S. officials as saying that most of these documents are original, but at least one appears to have been forged to indicate that Ukraine's losses outweigh Russia's, while the supposedly original document confirms the opposite.

  • What is the response of the authorities?

The U.S. Department of Justice has opened a criminal investigation, while the Department of Defense is assessing the potential consequences of the leak for U.S. national security.

The Pentagon said U.S. officials had reached out to Washington's allies about the matter, and relevant parliamentary committees had been briefed.

  • What are the consequences?

Pentagon spokesman Chris Meagher told reporters Monday that the online circulation of the documents poses "a very serious risk to the national security of the United States and may spread disinformation." The leak could put U.S. intelligence sources at risk, as well as provide Russia with valuable information on the situation of Ukrainian forces.

Documents dealing with U.S. partner countries could be an embarrassment for Washington, especially those that point to possible U.S. espionage on close allies.

  • Where did the documentation appear?

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

The investigative website Bellingcat said that some of these documents were circulating online before January 2023.

  • Who is behind the leak of documents?

U.S. officials are scrambling to determine the source of the leak, and Western security experts and U.S. officials say they suspect someone from the United States may have been behind the leak.

Officials say the breadth of the contents of the documents suggests they were leaked from a U.S. citizen, not an ally.