Two members of Russian punk group Pussy Riot have called on Australia to prevent their country's president, Vladimir Putin, from attending this year's G20 summit in Brisbane.

Nadezhda Tolokonnikova and Maria Alyokhina, who are in Sydney to speak at the Festival of Dangerous Ideas, spent 22 months in jail after staging a protest performance in a Moscow cathedral in 2012.

"We think that this person has no place at the G20," Ms Alyokhina told a packed Sydney Opera House audience through an interpreter.

This week Prime Minister Tony Abbott said calls to ban Mr Putin from the summit were weighing on his mind, given the current situation in Ukraine.

But he said G20 custodianship belonged to all member states equally and, as such, no one member state had the power to determine which others should and should not attend or how the summit was run.

"It's not a decision which Australia really has a right to make unilaterally," Mr Abbott told reporters on Friday.

If G20 member states were to agree to withdraw Russia's invitation, it would be the nation's second snubbing in three months.

In June, the US and its allies rescheduled a Group of Eight (G8) meeting to take place in Brussels rather than Sochi, meeting without Russia as the Group of Seven (G7).

In a joint statement, the G7 condemned the "continuing violation" of Ukraine's sovereignty by Russia.

Mr Abbott has described Russia's involvement in Ukraine as that of a bully and has warned Mr Putin he faces becoming an international outcast unless he keeps his forces within their borders.

"If, as seems to have been the case, Russian armed forces have simply moved across the border, that is an invasion and it is utterly reprehensible," he said.

Ms Tolokonnikova and Ms Alyokhina had almost completed their sentences when they were freed under a general amnesty in December.

Speaking at the festival, the pair said their performance could not take place now while the situation in Russia was so repressive.

"Unfortunately it wouldn't be even one second of our performance," Ms Alyokhina said, adding that a planned performance in Sochi during the Winter Olympics earlier this year was cut short by authorities.

"Now it's impossible to do anything."

Ms Tolokonnikova acknowledged that for some people in Russia their case had been an impetus for political activity.

"We have a voice and we hope that we use this voice correctly," she said.

ABC/AFP