Ukraine's security council secretary Oleksiy Danilov was dismissed and replaced by foreign intelligence service chief Oleksandr Lytvynenko under decrees published on the presidential website on Tuesday.
No reason was given for the change. Danilov had held the post since October 2019, a few months after President Volodymyr Zelenskiy took office.
Ukraine's National Security and Defence Council has a coordinating role on issues of national security and defense under the president. It comprises the country's top political, security and defense chiefs.
Zelenskiy has regularly replaced high-ranking security and defense officials since Russia's full-scale invasion in February 2022. The dismissal of Ukraine's top general in February presaged a wider clear-out of the military's top brass.
According to the president's website, Oleh Ivashchenko will be appointed as the new foreign intelligence chief.