Russia is pounding Ukraine's third-largest city ahead of a possible 32-hour truce aimed at pausing the fighting over Orthodox Easter.

An Orthodox Easter truce agreed by Russia and Ukraine came into force on Saturday afternoon but 38 minutes later we heard air raid sirens in Kharkiv region, northeastern Ukraine.

Ukrainian leader Volodymyr Zelenskiy, who has repeatedly ​proposed an Easter truce, quickly said Kyiv would abide by the measure, which Moscow had previously rejected as a " PR stunt ".