... and Ukraine vows to fight back.

Victoria Derbyshire and Gabriel Gatehouse reflect on this historic day... How did we get here? How did it all happen? And where could it be going?

We also speak to Vitaliy Shevchenko, the Russia editor at BBC Monitoring, and Askold Krushelnycky, a journalist in Ukraine.

Today's Ukrainecast was produced by Danny Wittenberg and Natalie Ktena. Emma Crowe was the technical producer. Sam Bonham was the assistant editor and Jonathan Aspinwall was the editor.