A new batch of classified documents that appear to detail American national security secrets from Ukraine to the Middle East to China has been reportedly leaked on social media sites.
The New York Times reported that the classified US military documents surfaced on social media on Friday.
The classified US military documents posted on social media offered a partial, month-old snapshot of the war in Ukraine, according to Reuters.
US officials alleged on Friday that Russia was behind that leak.
Russia or pro-Russian elements are likely behind the leak, three US officials told Reuters.
The officials, speaking on condition of anonymity, claimed that the documents appear to have been altered to lower the number of casualties suffered by Russian forces, adding their assessments were informal and separate from an investigation into the leak itself.
Reuters said Russian officials did not immediately respond to requests for comment.
The Pentagon said it is assessing the reported security breach but declined to comment on the authenticity of the documents circulating on sites including Twitter and Telegram, which are dated March 1 and bear markings showing them classified as "Secret" and "Top Secret."
"We are aware of the reports of social media posts, and the Department is reviewing the matter," Pentagon Deputy Press Secretary Sabrina Singh said.
A leak of such sensitive documents is highly unusual and would automatically trigger an investigation.
"We are aware of the reports of social media posts and the Department (of Defense) is reviewing the matter," Pentagon spokesperson Sabrina Singh said.
The Pentagon's review of the apparent leak was first reported by the New York Times.