KRAMATORSK, Ukraine

A large blast was heard in Ukraine’s capital Kyiv while at least two big explosions were heard in the city of Kramatorsk in the country’s eastern Donbas region early Thursday.

Kramatorsk is currently a city from where lots of foreign press members follow the latest developments on the line of contact.

Explosions were also reported in the cities of Kharkiv, Mariupol, Mykolaiv and Odessa.

Ukrainian local authorities said "the invasion has begun," adding that the explosions were "missile strikes."

No details were reported on casualties following the blasts.

Official statements on whether Russian troops had crossed the areas controlled by the pro-Russian separatists are yet to come.

Earlier, Russian President Vladimir Putin announced a special military operation in Donbas.