The office has been created "on the territories controlled by Ukraine", says its top military chief.
Ukrainian Gen Oleksandr Syrsky said the office would "maintain law and order" and "meet the immediate needs" of the population in the area.
In a video posted on social media, Gen Syrsky is seen telling a meeting chaired by Ukrainian President Volodymyr Zelensky that the office has been created "on the territories controlled by Ukraine".