A massive fire has broken out at a fuel storage facility in Crimea, which was unilaterally annexed by Russia in 2014. Moscow says the blaze was caused by a drone attack.

A blast occurred in the naval port city of Sevastopol on Saturday. The Russian-installed head of the region said an oil depot was hit by drones.

A senior Ukrainian military intelligence official told local media that a facility used by the Russian Navy's Black Sea Fleet had exploded. He described the blast as "God's punishment" for the killing of residents in Uman, a city in central Ukraine. He said the punishment will be long lasting.

The Ukrainian official was apparently referring to missile and drone attacks that Russia carried out on Friday.

Ukraine's Interior Minister Ihor Klymenko said on Saturday that two missiles had hit an apartment building in Uman. He said 23 people were killed, including six children.

In Russia, officials are preparing to stage military parades in Moscow and elsewhere on May 9 to mark the Soviet Union's triumph over Nazi Germany in World War Two.

But some regions near the border with Ukraine, and in the central part of the country, have cancelled their annual parades, citing security concerns.

Observers say the prolonged invasion is even affecting events aimed at boosting patriotism that Moscow considers important.