Mr Marles has pledged Australia will continue to back Ukraine as it resists Russian aggression.
"I don't think anyone imagined that Ukraine would stand up in the way that they have and and it has been heroic," he told ABC radio on Monday.
"I don't think there's anything inevitable about the outcome - this needs ongoing support."
Mr Marles, who is also the defence minister, said the west needed to fight for a rules-based order.
"It's completely unacceptable a large country seeks to impose itself on a smaller neighbour, not by reference to any international rule of law, but by reference to might and power," he said.
"That proposition simply can't stand."
Opposition foreign affairs spokesman Simon Birmingham said Australia needed to redouble its efforts.
"Australia's provision of weapons of vehicles, financial aid, humanitarian aid relief, all positioned us as the leading non-NATO contributor to the Ukraine cause right around the world," he told the ABC.
"We ought to make sure we continue that type of effort."
Senator Birmingham said the government needed to listen carefully to the type of support Ukraine was calling for and provide such assistance where possible.
"We've seen the US step up, Australia ought to be doing likewise," he said.
The war in Ukraine is expected to be on the agenda of a meeting between Chinese president Xi Jinping and Russia's Vladimir Putin at a summit in Uzbekistan this week.
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