Powerful explosions were heard in Kyiv early on Friday, and air raid sirens blared across Ukraine as residents braced for new Russian attacks after Moscow’s lead warship in the Black Sea sank following a fire. The explosions appeared to be among the most significant in Ukraine’s capital region since Russian troops pulled back from the area earlier this month in preparation for battles in the south and east. Ukraine claimed responsibility for sinking the Moskva, saying the Soviet-era flagship of Russia’s Black Sea fleet was struck by one of its missiles. The vessel sank late on Thursday as it w…