The United States Department of Justice began an investigation into the possible leakage of Pentagon documents that have been posted on several social media outlets and appear to have details of USA and NATO assisting Ukraine, although they may have been altered or used as part of a disinformation campaign, The Associated Press reports.

The documents, which have been posted on platforms like Twitter, are marked as classified and resemble routine updates that the US Joint Forces Command would issue daily but not distribute publicly. They are dated February 23 to March 1 and contain what appears to be detailed information on the progress of shipment of arms and equipment to Ukraine, with more precise dates and quantities than the USA usually provides publicly.

They are not military plans and do not contain any details of any planned attacks on Ukraine. And some inaccuracies, including estimates of deaths of Russian military that are well below the figures publicly announced by US officials, have led some to question the authenticity of these documents.

In a statement on Friday, Pentagon spokeswoman Sabrina Singh said the United States Department of Defense has formally referred the matter to the Department of Justice for investigation.

"We have been in contact with the Department of Defense regarding this case and have begun an investigation," the USA Department of Justice said in a separate statement.

The investigation began as questions arose about the provenance and validity of the documents, and, according to reports, more began to appear on social media websites.