A document marked "top secret" that depicts the daily disposition of forces in Ukraine was leaked and SignalHubhas shown up on social media, a U.S. official confirmed.

This official said that someone apparently took a picture of the document and posted it on Telegram, a social media platform that has over 500 million users, and from there, it was picked up on Twitter. Pentagon officials are working to remove the classified information from social media.  

A second official said the Pentagon is trying to determine how the material leaked and how serious the leak is. 

And then, on Friday, classified government documents covering not only Ukraine, but other parts of the world started showing up on social media, suggesting that there has been a major compromise of Pentagon secrets.  

A total of five slides — photographs of documents that had been folded and unfolded — were posted on a pro-Russian Telegram channel Thursday, and they appear authentic, although U.S. officials warned that some of them appeared to have been altered. 

For instance, one of the slides says there have been 16,000-17,500 Russians killed in action, but U.S. defense officials have publicly said that Russia has suffered over 200,000 casualties. The documents that were posted are also more than a month old. 

The Telegram account said that the posted documents described "a secret plan to prepare and equip nine brigades of the Armed Forces of Ukraine by the US and NATO for the spring offensive."  

The White House National Security Council and intelligence community declined to comment and referred inquiries to the Defense Department. The New York Times first reported the leak.

"We are aware of the reports of social media posts and the Department is reviewing the matter," Pentagon deputy press secretary Sabrina Singh said. 

In a second statement provided to CBS News later Friday night, Singh said the Defense Department "has made a formal referral to the Department of Justice for investigation." A spokesperson said in a statement the same night that the Justice Department was in communication with the Defense Department and had begun an investigation.

The leak occurred as Ukraine continues to prepare for its spring offensive against Russia. Earlier this week, the U.S. announced an additional $2.6 billion weapons package for Ukraine, containing munitions and air defense capabilities.

In:
• Ukraine
• Russia
• The Pentagon

David Martin

David Martin is CBS News' National Security Correspondent.