(This April 10 story has been corrected to read NOFORN instead of NONFORN, in paragraph 6)

WASHINGTON (Reuters) – U.S. national security agencies and the Justice Department are investigating the release of dozens of classified documents to assess the damage to national security and relations with allies and other countries, including Ukraine.

Here is what we know and do not know about what appears to be the gravest leak of U.S. secrets in years:

ARE THE DOCUMENTS REAL?

U.S. officials believe most of the materials are genuine. Some, however, appear to have been altered to show inflated U.S. estimates for Ukrainian battlefield casualties since Russia invaded in February 2022, as well as understated numbers for Russian forces.

It is unclear which of the documents might have been salted with misinformation and if they could be part of a Russian misinformation operation or a U.S. scheme to mislead Moscow about Kyiv’s war plans.

WHAT KINDS OF DOCUMENTS ARE THEY?

The documents, which are marked “Secret” or “Top Secret,” include sensitive briefing slides on how the war in Ukraine stood in February and March this year. On Monday the Pentagon said that the documents appear to be similar to the daily updates provided to its senior leaders as well as to other intelligence updates, though there appear to be some inaccuracies.

Classification markings on the materials include NOFORN, meaning they cannot be shared with foreign intelligence agencies.

The exceptions are materials also marked FVEY, or Five Eyes, referring to the spy services of the English-speaking nations of Canada, Britain, Australia and New Zealand. Materials marked that way would have been seen by thousands of people with security clearances.

But because not all of the documents are marked FVEY, U.S. officials believe whoever leaked them could be American.

Some documents are additionally marked FISA, meaning they were collected under the Foreign Intelligence Surveillance Act, the law that governs the U.S. monitoring of electronic communications.

HOW WERE THE DOCUMENTS LEAKED?

U.S. officials do not yet know how the documents found their way online.

Pictures of creased documents – suggesting that they might have been folded so they could be hidden before being removed from the top-secret spaces to which such materials are confined and photographed – were posted to social media sites.

Those platforms included Discord, an instant messaging platform popular with gamers, the online messaging board 4Chan, the encrypted Telegram global messaging app, and Twitter.

Although the documents only garnered widespread attention in the last few days, the open source investigation site Bellingcat said it had found evidence that the documents – or at least some of them – had appeared on social media as far back as March or even January.

In an article about the documents’ “improbable journey,” Bellingcat traced the earliest references to the leak to a now-defunct Discord server and cited three former users as saying that a large number of documents had been shared there.

WHAT DO THE DOCUMENTS SAY?

The documents cover a wide range of topics of interest to U.S. policymakers, including:

– Ukraine: Details about Ukrainian air strikes, the country’s air defense vulnerabilities, and even the size of some Ukrainian military units.

– Wagner group: Descriptions of a number of outreach efforts by the Russian mercenary group, including to Turkish “contacts,” Haitian government officials, and the organization’s growing presence in Mali.

– Middle East: Updates related to Iran’s nuclear activities as well as information about how the United Arab Emirates is in talks with Russia to help build a maintenance center for some weapons.

– China: Predictions about how China would respond to Ukrainian strikes inside Russia, along with details about British plans in the Indo-Pacific region.

– North Korea: Details about missile tests by Pyongyang and an assessment that a February parade likely oversold the ICBM threat to the United States.

– South America: Information about Brazilian officials’ plan to visit Moscow in April to discuss a Ukraine mediation scheme.

– Africa: An assessment that France is likely to struggle to achieve security goals in west and central Africa.

(Reporting by Jonathan Landay, Idrees Ali and Raphael Satter; Editing by Don Durfee and Rosalba O’Brien)

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