The online leaks of scores of highly classified documents about the Ukraine war present a "very serious" risk to national security, and senior leaders are quickly taking steps to mitigate the damage, a top Pentagon spokesman has said.
As the public airing of the data sends shock waves across the US government, the White House said there are concerns there could be additional leaks.
Chris Meagher, assistant to the Secretary of Defense for Public Affairs, told reporters Defense Secretary Lloyd Austin first became aware of the leak on Thursday local time.
In the days since, Mr Austin has reached out to allies, held daily meetings to assess the damage and set up a group not only to assess the scope of the information lost but review who has access to those briefings.
The department was looking closely at "how this type of information is distributed and to whom," Mr Meagher said.
A defence official who spoke to The Associated Press on the condition of anonymity to discuss sensitive matters said the Pentagon had now taken steps to reduce the number of people with access.
The official said the Pentagon regularly reviewed access lists, to decide who had a need to know and have access to classified material.
In an emailed statement to the ABC regarding the leak the Department of Foreign Affairs and Trade expressed the Australian government's concerns over the disclosure of US classified information.
"We are pleased the US Department of Justice has acted quickly in announcing an investigation. The Australian Government is seeking further information on this matter and is unable to provide further comment at this stage."
At the White House, National Security Council spokesman John Kirby was asked if the US was bracing for more online releases.
"The truth and the honest answer to your question is: We don't know," he said. "And is that a matter of concern to us? You're darn right it is."
Mr Kirby said at this point, "we don't know who's behind this, we don't know what the motive is".
He said as US authorities sifted through the documents posted online, they were still trying to determine their validity, but had found at least some of the papers had been "doctored."
He and others would not go into detail.
'Doctored' papers show lower Russian army deaths
At least one of the documents shows estimates of Russian troops deaths in the Ukraine war that are significantly lower than numbers publicly stated by US officials.
Under a section titled Total Assessed Losses, one document lists 16,000-17,500 Russian casualties and up to 71,000 Ukrainian casualties.
General Mark Milley, chairman of the Joint Chiefs of Staff, said publicly last November that Russia has lost "well over" 100,000 soldiers, and Ukraine had lost about that many also.
Those estimates have continued to climb in recent months, although officials have stopped providing more exact numbers.
At the State Department, spokesman Vedant Patel told reporters US officials were "engaging with allies and partners at high levels over this, including to reassure them of our commitment to safeguarding intelligence and the fidelity of securing our partnerships".
The US officials declined to provide any specifics, including about the expanse of the release, how it happened and to which country leaders the US has spoken.
Mr Patel added that there was "no question" the documents' release presented a risk to national security.
Investigators specialising in tracking social media, including at the journalism organisation Bellingcat, said the documents may have been circulating for months in private internet chats on the Discord discussion platform.
Asked if the Pentagon had contacted Discord, Mr Meagher referred questions to the Justice Department, which has opened a criminal investigation into the leaks.
'Potential to spread misinformation' in documents
The slides, which eventually were distributed on more mainstream sites such as Twitter, detail US training and equipment schedules to support Ukraine, assessments of losses, what the US is monitoring on key allies and strategic partners, and what moves Russia may be taking to undermine those relationships.
While the Pentagon has been careful not to authenticate the information contained in any specific document, overall "they present a very serious risk to national security and have the potential to spread disinformation," according to Mr Meagher.
"We're being very careful and watching where this is being posted and amplified."
The documents are labelled Secret and Top Secret and in some cases resemble routine updates that the US military's Joint Staff would produce daily but not distribute publicly.
ABC/AP
