What do the documents show?
Broadly speaking, the leak contains detailed assessments of the situation on the battlefield in Ukraine as well as information on support from Western countries.
Most documents are dated to early March. Here is a selection of what they are stated to contain:
• Information about military resources on both the Ukrainian and Russian sides as well as plans for how the US and NATO can build up the Ukrainian defense for an upcoming offensive.
• Data on Ukraine's air defences. In one document, it is estimated that the system will be completely eliminated within a month if it continues to be used to the same extent.
• Details of internal discussions between South Korean officials regarding arms support to Ukraine. The information is allegedly based on signals intelligence, which has raised suspicions that the US may have been spying on them. A spokesperson for South Korea's president told Reuters it was investigating the allegations and would take "appropriate action."
• Information about the Israeli security service Mossad, also obtained through signals intelligence.
Can the content be trusted?
The Pentagon declined to comment on the authenticity of the documents, citing an ongoing investigation.
Military analysts, however, are united in saying that at least some of them have been disguised in Russia's favor. Among other things, the number of Russian losses seems to have been written down, writes the New York Times.
At the same time, the documents seem to have consequences regardless of authenticity. Ukraine has already reversed parts of its military plans as a result of the leak, a source close to Zelenskyy told CNN.
Who is behind it?
Several experts see it as most likely that the leak is an American, Reuters writes.
"A lot of the documents have just been in American hands," former Pentagon employee Michael Mulroy told the news agency.
Other government sources told Reuters that it could not rule out that Russia or pro-Russian actors published the documents. Ukraine completely dismisses the leak, saying it is part of Russian propaganda.
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"Hard to judge how credible they are." Hear Lieutenant Colonel Joakim Paasikivi about the leak from inside the Pentagon. Photo: Susan Walsh/TT