Blasts heard in Russian city, Ukraine's key port bombed: Report

The blasts come days after Russia's defence ministry said two Ukrainian helicopters struck a fuel depot in the city, some 35 km from the border with Ukraine, after entering Russia at low altitude.

Russian attacks have destroyed an oil refinery in the central Poltava region and struck “critical infrastructure”, most likely oil facilities, near the port city of Odesa, local officials said on Sunday.

Russian forces have attacked Odesa, the main base for Ukraine's navy, alongside other Ukrainian Black Sea ports such as Mariupol and Mykolaiv. If taken, it would give Russia a land corridor from Crimea to Transniestria, a Russian-speaking breakaway province of Moldova that hosts Russian troops.

Oil facilities have been a focus of attacks.

Dmytro Lunin, governor of the Poltava region, said on television that the refinery had been destroyed in a rocket