KYIV, Ukraine (AP) — A drone-borne explosive device detonated Sunday at the headquarters of Russia’s Black Sea Fleet, injuring six people, officials said.

The explosion at the headquarters in the city of Sevastopol on the Crimean peninsula that Russia annexed from Ukraine in 2014 caused cancellation of observances of Russia’s Navy Day holiday.

The Black Sea Fleet’s press service said the drone appeared to be homemade. It described the explosive device as “low-power” but Sevastopol mayor Mikhail Razvozhaev said six people were injured in the blast.

There was no immediate information on where the drone began its flight; Sevastopol is about 170 kilometers (100 miles) south of the Ukrainian mainland and Russian forces control much of the mainland area along the Black Sea.

Fighting continued elsewhere in Ukraine. The mayor of the major port city of Mykolaiv, Vitaliy Kim, said one person died in Russian shelling that damaged a hotel and school buildings.

In the Sumy region in Ukraine’s north, near the Russian border, shelling killed one person, the regional administration said.

Three people died in attacks over the past day in the Donetsk region, which is partly under the control of Russian separatist forces, said governor Pavlo Kyrylenko.