Summarize this text:


Highly classified Pentagon documents leaked online in recent weeks have provided a rare window into how the US spies on allies and foes alike, deeply rattling US officials, who fear the revelations could jeopardize sensitive sources and compromise important foreign relationships.

Some of the documents, which US officials say are authentic, expose the extent of US eavesdropping on key allies, including South Korea, Israel and Ukraine.

Others reveal the degree to which the US has penetrated the Russian Ministry of Defense and the Russian mercenary organization NAME_1 Group, largely through intercepted communications and human sources, which could now be cut off or put in danger.

Still others divulge key weaknesses in Ukrainian weaponry, air defense, and battalion sizes and readiness at a critical point in the war, as Ukrainian forces gear up to launch a counteroffensive against the Russians – and just as the US and Ukraine have begun to develop a more mutually trusting relationship over intelligence-sharing.