Ukraine crisis: Russia assaulting Ukraine, says Obama

US President Barack Obama has condemned what he called a "brazen assault" on Ukrainian sovereignty by Russia.

Mr Obama said "Russia's aggression" was threatening European peace, and asserted that countries' borders would not be re-drawn "at the barrel of a gun".

Russian President Vladimir Putin has said he is hoping for a peace agreement to be reached by Friday, and has denied supporting pro-Russia separatists.