Australian Greens leader Christine Milne is demanding Prime Minister Tony Abbott intervene at the highest level to obtain the release of an Australian activist from a Russian jail.

"I am calling on Tony Abbott to pick up the phone to President Putin and seek the release of Colin Russell," she told reporters in Sydney.

Mr Russell, 59, is one of 28 international activists and two journalists being held by Russian authorities following a Greenpeace protest against oil drilling in the Arctic in September.

Senator Milne said other countries were taking the detention of their citizens more seriously than Australia, citing the example of UK leader David Cameron who had undertaken to talk to Mr Putin.

She warned Mr Russell might be relocated to another prison in Russia.

"At the very least we need a letter of guarantee which would enable him to get bail."