Ukraine's acting leader says his country's on the brink of disaster and is urging Russia to withdraw its troops.

The Kremlin's authorised military action on Ukrainian soil, claiming Moscow has a right to protect its interests.

Kiev warns Vladimir Putin's actions amount to a declaration of war.

NATO says Russia is threatening peace and security in Europe.

Its General Secretary, Anders Fogh Rasmussen, says Russia is threatening peace and security in Europe and should de-escalate tensions.