welcome back to our breaking news coverage. i'm rosemary church. an empty airspace over ukraine as the crisis sharply escalates on the ground. this radar showing no signs of any aircraft after aviation authorities restricted the country's airspace. russia also issued a notice banning civil aircraft from flight routes along ukraine's border. ukrainian officials say attacks from russian troops have come from russia, belarus, and crimea, and you're looking at video now of military vehicles entering ukraine from a border crossing with crimea. cnn correspondents have heard explosions in cities across ukraine, including near kyiv, kharkiv and odessa. ukraine's defense minister insists the situation is under control and that russian troops are suffering losses.