A Russian court has granted bail to Australian Colin Russell, the last of 30 Greenpeace crew members detained since their September protest against Arctic oil drilling.

The decision to free the ship’s radio operator reversed an earlier ruling extending his detention, which was given just before all the other members of the Arctic Sunrise crew were released.

“Excellent news! Colin Russell from Australia is granted bail,” the global environmental protection group tweeted in a message that was confirmed by Russian news agency reports from the Saint Peterburg court.

The Greenpeace protest targeted Russia’s first oil rig in the Arctic – a politically sensitive region that President Vladimir Putin views as the future of the country’s energy exporting might.

Irate Russian authorities initially accused the crew – two of whose members unsuccessfully attempted to scale the platform – of piracy before reclassifying the offence to the less serious charge of hooliganism.

Thursday’s ruling came after a St Petersburg judge on November 18 ordered that Russell, 59, remain in pre-trial detention until February 24 – a day after the end of Russia’s Winter Olympic Games in the Black Sea resort of Sochi.

That decision sparked concern that Russia intended to take a tough line with the other members of the mostly foreign crew, despite international pressure to release them.

Officials never explained their apparent change of heart. But some analysts speculated that Russell’s initial bail hearing was held before judges had received Kremlin instructions to go easy on the crew in the face of the developing diplomatic scandal.

The court’s decision on Thursday has been met with relief by Russell’s family and a stern determination to keep fighting the charges by Greenpeace itself.

“I am so relieved that my beautiful, peaceful man will soon be out of detention,” Russell’s wife Christine said in a statement released by Greenpeace.

“It remains a really difficult time and only when all of the Arctic 30 are free to go home will we be able to properly celebrate,” she added.

The icebreaker’s crew comprised nationals from 18 countries besides Russia and it remains unclear when the foreigners will be allowed to go home.

The hooliganism charges the crew still face carry seven-year sentences and the foreigners have been forced to stay in a St Petersburg hotel pending trial – should one still take place.

Kremlin chief of staff Sergei Ivanov says the foreigners may actually be allowed to leave the country “as soon as the issue of how they can leave Russia is resolved”.

Russian media said the problem hindering the crew members’ departure is their lack of Russian visas.

Greenpeace says Russell will be released from prison as soon as the court accepts the organisation’s two-million-ruble ($A66,000) bail payment.

The Kremlin last week rejected a separate decision by an international maritime tribunal in Germany for Russia to return the Dutch-flagged icebreaker to Greenpeace.