MOSCOW — In a sweeping military shake-up, Russia has replaced the top commanders of its Baltic Fleet, which patrols a region that has become the main fault line between Russia and the West.

The exact reasons for the mass dismissal, involving dozens of officers, remain unclear. But the public nature of the abrupt change, announced on Wednesday by Defense Minister Sergei K. Shoigu, was unprecedented.

The fleet commander, Vice Admiral Viktor Kravchuk; his chief of staff, Vice Admiral Sergei Popov; and the other officers were fired for “dereliction of duty” and “distortion of the real state of things,” according to a statement by the Defense Ministry summarizing what the minister had said behind closed doors to senior military commanders.

The statement went on to say that the commanders had been responsible for “serious drawbacks in the organization of military training and everyday activities” and “lack of proper care for the personnel.”