President Vladimir Putin says Russia has reserved the right to use all options in Ukraine, but that Moscow would use force only as a last resort.
Arseny Yatseniuk says the announcement to invade Ukraine made by Russia's Vladimir Putin was not a threat, but "the declaration of war to my country".
Russian President Vladimir Putin has cited a threat to Russian citizens and servicemen at its Black Sea fleet as a need to send in armed forces.
One Olympic ring failed to unfurl but President Vladmir Putin nonetheless declared Russia's Winter Games open under a burst of fireworks.
President Vladimir Putin has ordered tighter security from law enforcement agencies after a second bomb exploded in the country in just three days.
The US, UK and France want UN-sanctioned use of force should Syria fail to allow destruction of its chemical weapons, but Russia disagrees.
Despite France's sentiments, Russia's foreign minister has said there was no proof that Bashar al-Assad's troops carried out the attack on Damascus.
Fugitive former US spy agency contractor Edward Snowden slipped out of Moscow's Sheremetyevo airport after Russia granted him temporary asylum.
Russia's scientists believe they have discovered new life forms sealed off for millions of years in a subglacial lake deep under the Antarctic ice.
President Vladimir Putin has signed a law that bans Americans from adopting Russian children and imposed other sanctions in retaliation.