Russia on Thursday claimed it has destroyed Ukraine's air defence system and air bases in a military attack on the West-backed neighbouring country.
Ukraine on its part claimed that its forces downed 5 Russian warplanes and a helicopter as its forces fought back the Russian attack.
Russian military has said that it has attacked Ukrainian military targets and no populated areas have been attacked.
Russian President Vladimir Putin on Thursday morning cleared military action in Ukraine.
Kyiv claimed that it has been been attacked from three sides with Crimea and Belarus forces joining Russian military.
Hundreds of Ukrainian service members are believed to have been killed in Russian attacks, a Ukrainian official has been quoted as saying by the Wall Street Journal.
Big explosions have been reported from many cities in Ukraine including the Capital Kyiv.