MOSCOW — A group of Ukrainian hackers has released what it says are the emails of a senior Kremlin official that show a direct Russian role in creating and directing the rebel uprising in eastern Ukraine in 2014.

The group claimed to have hacked the account of Vladislav Y. Surkov, for years President Vladimir V. Putin’s chief domestic political adviser and now the top official overseeing Russia’s Ukraine policy.

The group released what it says are thousands of letters to and from Mr. Surkov’s office email account, adding a fat dossier to this year’s vast spill of emails around the world and showing high-level Kremlin meddling in Ukraine.

While the authenticity of the documents has yet to be fully established, several of the people who corresponded with Mr. Surkov confirmed that the messages of theirs released by the hackers were the ones they sent.