Russian President Vladimir Putin on Thursday announced a “military operation" in Ukraine's Donbas region.
"We are hearing reports - some unconfirmed - of explosions in other parts of Ukraine. Loud bangs in the capital Kyiv as well as Kramatorsk in the Donetsk region," BBC News reported.
A huge military convoy of more than 100 military trucks with soldiers was also seen heading towards the Ukrainian border where 190,000 Russian troops are already massed, raising fears Putin is about to stage a land-grab in eastern Ukraine, the report said.
Putin has already moved more than 10,000 Russian troops into Ukraine's breakaway eastern regions of Donetsk and Luhansk after he recognized them as an independent.
Some 6,000 troops were sent to Donetsk, 5,000 to Luhansk and 1,500 to the city of Horlivka, a source with links to Ukrainian intelligence said.
Pictures and videos from Ukraine widely circulate on Twitter.
In 2014 soon after Russia annexed the Crimean Peninsula, the regions of Donetsk and Luhansk proclaimed their independence.
Peace agreements were signed during 2014-15, but the conflict remained which led to hundreds of thousands of people leaving the regions.
An estimated 14,000 people have died since 2014.