KYIV (AFP) - Explosions rang out before dawn on Thursday (Feb 24) in Ukraine's capital Kyiv and several cities near the front line 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 35km south of the Russian border.

Four loud blasts rang out in Kramatorsk, a front-line 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.

Russia is targeting Ukraine’s military infrastructure, air defence and air forces with high-precision weapons and is not attacking Ukrainian cities, Russia’s RIA news agency cited the Russian Defence Ministry as saying.

Ukraine closed its airspace to civilian planes, and Foreign Minister Dmytro Kuleba tweeted that his country was facing a "full-scale invasion"'.