The Justice Department has opened an investigation into reports that a trove of apparently classified U.S. intelligence documents was leaked online from the Pentagon, the Defense Department said on Sunday night.

Driving the news: Pentagon deputy press secretary Sabrina Singh said in an emailed statement that officials are assessing the validity of the material, which the New York Times reports indicates that U.S. intelligence has penetrated Russia's military and also apparently spied on allies including Israel, South Korea and Ukraine.

• Although apparently classified photos began circulating on Russian Telegram channels last week, investigative journalism group Bellingcat notes they emerged on the platform Discord in early March and some documents may have been posted in January.

State of play: Singh said U.S. Defense Department officials are reviewing and assessing "the photographed documents that are circulating on social media sites and that appear to contain sensitive and highly classified material."

• An interagency effort was now focused on assessing the impact these documents could have on U.S. national security, as well as American allies and partners, Singh said.
• "Over the weekend, U.S. officials have engaged with Allies and partners and have informed relevant congressional committees of jurisdiction about the disclosure," she added.
• "The Department of Defense's highest priority is the defense of our nation and our national security. We have referred this matter to the Department of Justice, which has opened a criminal investigation."
• Representatives from the DOJ did not immediately respond to Axios' request for comment.