Citing senior officials, the New York Times reported the documents were leaked on Twitter and Telegram and represent a significant breach of US intelligence.
The documents reportedly contain information of anticipated weapons deliveries, US estimates of Ukrainians and Russians killed in the conflict, and force strength estimates, but no specific battle plans.
The documents are from March 1 and depict US and Ukrainian perspectives of what is needed for the counteroffensive, but there were no details about when or where Kiev would launch its operation, according to the report.
The report said the documents outline that 12 Ukrainian combat brigades are being assembled with nine of them apparently being trained and supplied by the United States and other NATO countries. The documents also claim that more than 250 tanks and more than 350 vehicles would be needed.
Moreover, the report said the documents show the expenditure rate of US-supplied HIMARS munitions, which had not been previously disclosed by the Pentagon.
The US administration, as of Thursday evening, has unsuccessfully tried to get the documents deleted on the social media platforms, the report added.