Russia has replaced the commander of its Crimea-based Black Sea Fleet after a series of explosions rocked the peninsula it annexed in 2014 and had previously seen as a secure rear base for its war in Ukraine.

Moscow blamed saboteurs for blasts that engulfed an ammunition depot in northern Crimea on Tuesday. Plumes of smoke were later seen rising at a second Russian military base in central Crimea, Russia's Kommersant newspaper said.

Ukraine has not officially taken responsibility but has hinted at it. The apparent Ukrainian capability to strike deeper into Russian-occupied territory, either with some form of weapon or with sabotage, indicates a shift in the conflict. Blasts destroyed warplanes at a Russian naval airbase in Crimea last week.

On Wednesday, Russia's RIA news agency cited sources as saying the commander of its Black Sea fleet, Igor Osipov, had been replaced with a new chief, Viktor Sokolov.

If confirmed, the move would mark one of the most prominent sackings of a military official so far in a war in which Russia has suffered heavy losses in men and equipment.

State-owned RIA cited the sources as saying the new chief was introduced to members of the fleet's military council in the Crimean port of Sevastopol.

The Black Sea Fleet, which has a revered history in Russia, has suffered several humiliations since President Vladimir Putin launched what Moscow calls a "special military operation" on February 24.

In April, Ukraine struck its flagship, the Moskva, a huge cruiser, with Neptune missiles. It became the biggest warship to be sunk in combat for 40 years.

Crimea, which Russia seized from Ukraine in 2014 and has extensively fortified since then, provides the main supply route for Russian forces in southern Ukraine, where Kyiv is planning a counter-offensive in coming weeks.

Ukrainian military intelligence said in a statement that after the recent explosions in Crimea, Russian forces had urgently moved their some of their planes and helicopters deeper into the peninsula and to airfields inside Russia. Reuters could not independently verify the information. (Reuters)