Russia meanwhile said power and energy facilities had been targeted overnight by Ukraine, which has not commented.

President Donald Trump has sent a letter of support to Ukraine praising its courage and saying the United States believes in its future as an independent state, as the country marks the anniversary of declaring itself free of Soviet rule.

It comes as Ukraine is celebrating its independence day on Sunday, which marks the country's declaration of independence from the Soviet Union in 1991. The United Nations' International Atomic Energy Agency (IAEA) has repeatedly called on both Russia and Ukraine to show maximum restraint around nuclear facilities in the war.

Volodymyr Zelensky urges Western allies to impose fresh sanctions on Moscow if it shows no interest in peace.

Russia’s top diplomat said in an interview released on Friday that “there is no meeting planned” between President Vladimir V. Putin of Russia and President Volodymyr Zelensky of Ukraine. It was the Kremlin’s most direct declaration yet that a summit the White House suggested was imminent was nowhere close to materializing.