US President Donald Trump said he hoped to avoid military action against Iran, which has threatened to strike American bases and aircraft carriers in response to any attack.
Ukraine's state weather agency on Thursday forecast a drastic dip in temperatures to as low as minus 30C in coming days as authorities race to restore services.
Videos filmed by local people showed streaks of light in the sky with the sound of loud explosions, while other images showed flames several metres high and charred cars.