Ukraine has changed some of its military plans following a leak of dozens of Pentagon documents, a source close to Ukrainian President Volodymyr Zelensky told CNN.

The documents are part of a trove of U.S. and NATO intelligence documents that were  leaked over the past couple of months, appearing on the social media platform Discord.

The leaked documents, the source of which remains unknown, provide a grim assessment of the strength of Moscow’s war machine. But the information also suggests the Ukrainian military is in dire straits, too. Among other things, some of the documents  outline critical shortages of Ukrainian air defense munitions.

While Ukrainian officials have  dismissed the documents as "fake," U.S. officials have confirmed to both the New York Times and CNN that the documents are legitimate although some of them appear to have been altered.

CNN quoted Mykhailo Podolyak, an adviser to the head of the Office of the President of Ukraine, as saying on Telegram on April 7 that he believed the documents are "based on a large amount of fictitious information" and have "nothing to do with Ukraine's real plans."

The documents also reveal that the U.S. has been spying on President Zelensky, which has deeply frustrated Ukrainian officials, the source close to the president told CNN.