In a day of fast-moving developments, there are reports that columns of Russian armoured vehicles have begun rolling across the border.

Earlier Russian President Vladimir Putin gave the order for so called "peacekeepers" to enter two separatist regions of Ukraine which he's recognised as "independent states".

The events dramatically increase tensions in eastern Europe with western leaders condemning Russia's move as a violation of Ukraine's sovereignty and international law and vowing to retaliate with sanctions.

ABC The World Today reports on the latest developments and includes comments from USSC senior lecturer Gorana Grgic.