He's dismissive of Vladimir Putin's claim that he is sending troops to separatist areas for a peacekeeping mission.
The "suggestion they are peacekeeping is nonsense", he says.
He says he hopes that diplomatic efforts can avoid a violent confrontation and says he will be "in lock-step" with other countries in quickly putting in place sanctions on Russia.
"Russia should step back. It should unconditionally withdraw. It's unacceptable, it's unprovoked, it's unwarranted," he says.