A senior Ukrainian official has stressed that the country has reached a phase of taking the offensive to take back territories captured by Russia, including Crimea.

Ukraine's presidential adviser Mykhailo Podolyak gave an exclusive interview to NHK in Kyiv, on Tuesday.

He said the Ukrainian military are using weapons provided by the United States and other Western nations to focus on destroying Russia's arms depots, fuel storage facilities and strategic command posts to drive Russia into withdrawal.

He said the aim of the battle is to fully restore the internationally-recognized borders of Ukraine.

He did not make clear whether Ukraine was directly involved in a series of explosions in Crimea this month. Russia annexed the peninsula eight years ago.

He said, however, the incident indicates that the goal of operations in Crimea will be the same as those being carried out in other parts of the country, including its south.

He acknowledged that Russia is superior in terms of fire power, as it has large amounts of rockets and long-range artillery.

He said, if 50 more US-made HIMARS rocket systems are to be supplied, for example, the speed of Ukraine recapturing its territories would be substantially accelerated.