The Australian Federation of Ukrainian Organisations says Russia's decision to recognise the control of "terrorist organisations" in Luhansk and Donetsk is provocative and dangerous.
"Such a step is another act of aggression against Ukraine, its independence, sovereignty and territorial integrity," AFUO co-chair Stefan Romaniw said.
"It demonstrates Russia's decision to choose a path of global isolation and aggression against the international rules-based order."
Mr Romaniw said resistance in Ukraine has grown since the 2014 annexation of Crimea and civil society remained strong.
"I have spoken today to Ukrainians in Odessa, and they have told me that on the street, at every intersection, in every building and every house, Putin will find resistance," he said.
"We are ready to fight."
Mr Romaniw also called for punitive and personal sanctions against the Russian president himself, just hours after Prime Minister Scott Morrison formalised sanctions that targeted eight members of Russia's security council.
Mr Morrison was asked directly about sanctions targeting Mr Putin when he announced the sanctions on Wednesday, responding "we will continue to ratchet this up over time".
Save the Children has warned that children will bear the brunt of any conflict with 40,000 children making up a large part of the 100,000 people who've been displaced in eastern Europe in recent days.
The organisation says any mass movement will put children in danger of hunger, cold and illness as well as losing limbs and their lives from explosive devices, with eastern Ukraine being "one of the most mine-contaminated regions in the world".
"Children are terrified – they wonder if their homes will be shelled, their friends hurt, their security and sense of normalcy lost," Save the Children's eastern European director Irina Saghoyan said.
"This is an appalling situation. But more fighting isn't inevitable. Leaders must step up, in the interests of the region's most vulnerable, its children."
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