The Pentagon said it was “working around the clock” to determine the source and scale of a leak of highly classified intelligence documents that appear to contain operational data on the war in Ukraine and information from countries in Asia and the Middle East.
“We’re still investigating how this happened, as well as the scope of the issue,” Chris Meagher, assistant to the secretary of defence for public affairs, told reporters on Tuesday. “There have been steps to take a closer look at how this type of information is distributed and to whom.”
The Department of Justice has opened a criminal investigation into the leak of dozens of documents as American officials try to understand what ramifications it could have on the battlefield in Ukraine and on US efforts to gather intelligence.
Defence officials said they are still trying to establish the scope of the leak but confirmed dozens of documents did appear to contain sensitive and highly classified information. The files first appeared on messaging platform Discord in January and more recently circulated to other social media including Twitter and Telegram.
The breach — which appeared to be the most significant since Edward Snowden released a trove of classified documents about US intelligence activities a decade ago — included apparently highly classified documents. Officials have said they appear mostly authentic, and cover a range of topics, mainly relating to Russia’s full-scale invasion of Ukraine.
Current and former officials said the photographs of printed pages of intelligence briefings and slides appeared to have been prepared for a briefing book for a senior official. It was not immediately clear who the official in question was.
“These photos appear to show documents similar in format to those used to provide daily updates to our senior leaders on Ukraine and Russia-related operations as well as other intelligence updates,” Meagher said, adding that some appeared to have been doctored.
John Kirby, US National Security Council spokesman, said President Joe Biden was first briefed on the leak “late last week” and had been in contact with national security officials “throughout the weekend”.
Kirby said: “We don’t know who is behind this. We don’t know what the motive is . . . we don’t know what else might be out there.
“We know that some of them have been doctored . . . we are still working through the validity of all of the documents that we know are out there.”
Some of the materials appear to have been specifically prepared by the Joint Staff at the Pentagon. Others seem to be documents included in daily briefings for national security officials. Other than the war in Ukraine there are references to China, Iran, South Korea and Israel.
The documents point to important challenges for both Ukraine and Russia, and purport to show that both countries face setbacks in training and equipping troops. However, they appear to indicate that Ukraine’s air defences are particularly vulnerable and the country has a dwindling supply of missiles that have so far kept Russia from boosting the role of its air forces in the war.
“This is bad news for everyone,” a European official said. “It’s bad news for the Ukrainians, it’s bad news for the Americans because everyone sees how they operate, and its bad news for the allies more generally because we see that the Ukrainians are running out of ammunition, which is not the best message you want in the air.”
The 50 pages of documents reviewed by the Financial Times also indicate that American intelligence has penetrated Russian military officials at the highest level and can gain information to inform Ukrainian decisions on a daily basis.
The documents, the most recent of which are from early March, have sown chaos and paranoia among Washington’s national security apparatus ahead of a critical moment in the Ukraine war. Kyiv’s forces are soon expected to launch a counter-offensive against Moscow.
Officials have said their efforts to trace the origin of the leak have been complicated by the fact that the documents appear to have been printed out and photographed.
“The documents reveal how good US intelligence is and the extent to which it has penetrated Russian agencies,” said Dan Lomas, lecturer in intelligence and security studies at Brunel University in London.
“An insider job is far more likely,” added Lomas, referring to the theory that an American citizen was involved in the leak. “The enemy within is always the bigger threat.”
Current and former officials said the release could jeopardise not only information critical to American policymaking, but also potentially the safety of individuals who provide intelligence.
Some of the revelations sparked discontent and denials among allies, including one report from intercepted communications suggesting leaders of Israel’s Mossad intelligence agency encouraged the recent protests against prime minister Benjamin Netanyahu.
Israel’s government’s said in a statement on behalf of Mossad that the assertion was “mendacious and without any foundation whatsoever”.
The leaked material also appeared to contain details of internal deliberations by South Korean officials over whether to send ammunition to the US, which might be passed on to Ukraine. Seoul has resisted pressure from western officials to give military assistance to Ukraine.
British officials also pushed back against a description in the documents of an October episode involving a British surveillance plane that was allegedly nearly shot down by a Russian fighter jet.
“These reports contain inaccuracies and do not reflect what happened in International air space over the Black Sea,” a British defence source said.
Additional reporting by James Shotter in Jerusalem and Christian Davies in Seoul