Greens leader Richard Di Natale says it's inconceivable his party could support a minority coalition government.
Recent opinion polls have raised the prospect of a hung parliament after the July 2 federal election.
Asked at the National Press Club on Wednesday whether the Greens could support a Liberal-Nationals minority government, the leader said: "It's inconceivable that we could form a robust coalition with the government."
The coalition's views on climate change, refugees and standing in the way of the shift to the "new economy" would prevent the Greens from backing it in government.
If Labor was to form a minority government "ultimately it will be up to Labor to decide if they want to have a conversation with us".
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The previous agreement with the Gillard government in 2010 had been "very effective", delivering climate laws and a dental scheme, Senator Di Natale said.
