Russia has appointed a new commander for its operations in Ukraine as it refocuses its war effort in the east, having failed to secure territory around the capital, Kyiv.

Known for his brutality, General Alexander Dvornikov, commander of the Southern Military District, will now lead Russian troops on the ground, according to Western security officials and diplomats with knowledge of the change. The Kremlin has not announced the appointment.

Dvornikov, 60, has held several senior positions in the Russian military, including army commander of the Far Eastern Military District. He notably oversaw Moscow’s forces in Syria in 2015 and 2016, where they fought alongside Syrian government troops in a conflict in which President Bashar al-Assad was accused of using chemical weapons against his people...