Anonymous said it obtained the data from a server at the Bundestag or German parliament. The group has claimed responsibility for a series of leaks of confidential data worldwide in the past year.
The military documents were collected for an inquiry, now finished, into a September 2009 airstrike by US jets under German orders that killed more than 140 Taliban fighters and Afghan civilians.
Omid Nouripour, a Green Party legislator who was on the inquiry committee, told dpa the documents posted online were authentic. He said he had not seen anything in the online version that would put lives in danger.
The Bundestag administration said it was checking the leak. A spokeswoman said it was possible the documents had been merely appendices to the inquiry’s report.
The inquiry criticized the 2009 airstrike.