Ukrainian Defense Minister Oleksii Reznikov submitted a letter of resignation after President Volodymyr Zelenskyy said he would be replaced and named his successor.
Russian officials are accusing Ukraine of launching what appears to be the biggest nighttime drone attack on Russian soil since the war began 18 months ago.
The shelling followed the severe damage sustained by a beloved Orthodox cathedral in a missile strike last week in Odesa and underlined the war's risk to the country's cultural monuments.