On Sunday, Ukraine hit Russia's second city as its ties with Washington strained in recent days. Kyiv says its retaliatory strikes are fair retribution for years of Russia's offensive and destruction of its energy infrastructure Key points and original sources are listed below.

• On Sunday, Ukraine hit Russia's second city as its ties with Washington strained in recent days.S1

• Kyiv says its retaliatory strikes are fair retribution for years of Russia's offensive and destruction of its energy infrastructureS2