Russia's full-scale invasion of Ukraine is now into its fourth day.

The war has triggered a humanitarian crisis, with hundreds-of-thousands of people fleeing their homes - more than 150,000 have already made it across the border to Poland.

Overnight, Russia put its nuclear forces on high alert.. as it continues its push into Ukraine.

Globally, governments, businesses and banks are bracing for cyber warfare.

But Ukrainians are fighting back -- the government's Defence of Ukraine account tweeted they had killed or wounded more than 4000 Russian soldiers.

This week, the United Nations' general assembly of 193 countries will debate Russia's invasion.

The director of Massey University's Centre for Defence and Security Studies, Professor Rouben Azizian, was in the Soviet and later Russian Foreign Service.

Professor Azizian spoke to Māni Dunlop about what peace could cost Ukraine.