Explosions rang out before dawn Thursday in Ukraine's capital Kyiv and several cities near the frontline and along the country's coast, after Russian President Vladimir Putin announced a military operation.
AFP correspondents also heard blasts in the Black Sea port city of Odessa, with police and ambulance sirens heard across the Ukrainian capital city.
Explosions also rang out in Kharkiv, a large city 35 kilometres (20 miles) south of the Russian border.
Four loud blasts rang out in Kramatorsk, a frontline city that serves as the Ukrainian government's effective capital for the eastern war zone, and more were heard in the eastern port city of Mariupol, AFP reporters said.
Ukraine closed its airspace to civilian planes, and Foreign Minister Dmytro Kuleba tweeted that his country was facing a "full-scale invasion"'.
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