Russian President Vladimir Putin on Thursday authorised a "special operation" in Ukraine's Donbass region, Russian state news agency TASS reported.
Appearing in a televised address on Russian TV, Putin has also urged the Ukrainian soldiers in eastern Ukraine to lay down weapons and return to their homes. He cited 30 years of failed negotiations over Ukraine's blackmail to join the NATO forces.
Several reports have confirmed that the operation has already begun. "We are hearing reports - some unconfirmed - of explosions in other parts of the Ukraine. Loud bangs in the capital Kyiv as well as Kramatorsk in the Donetsk region," BBC news reported.
But there have also been reports on social media of explosions in Ukraine's Kharkiv in the north-east, Odesa in the south, and the eastern Donetsk Oblast area.
In his televised speech, Russian President Putin has warned other nations of consequences if they interfere. Ukraine has imposed emergency a few hours before the announcement of Russian military offensive by Putin.
(With inputs from agencies)