A Russian court on Monday extended the pre-trial detention of one of 30 Greenpeace activists arrested for a protest against Arctic oil drilling, but unexpectedly freed a Russian doctor on bail.

Yekaterina Zaspa, a doctor with Greenpeace's Arctic Sunrise icebreaker, became the first of the arrested crew members to be freed pending trial, after two months in detention.

She will be released on bail of two million rubles ($61,400, 45,500 euros), Greenpeace said, citing the ruling of the Kalininsky court in Russia's second city of Saint Petersburg.

"She may be released on bail, but she is still charged with hooliganism, the charge of piracy has not been officially withdrawn, and therefore she still faces maybe 20 years in jail for a crime she didn't commit," Greenpeace's Mads Christensen said in a statement.

The 30 activists from 18 countries were first charged with piracy, which carries a maximum sentence of 15 years. The charges were later changed to hooliganism, which carries a punishment of up to seven years.

But, in another sign of hope for the detainees, a prosecutor said Monday he was not against another activist, Ana Paula Maciel from Brazil, also being freed, Greenpeace said.

Judges in Russia often side with the prosecution.

A decision on Maciel's fate will be announced on Tuesday.

Earlier on Monday, another Saint Petersburg court extended the pre-trial detention of Australian activist Colin Russell until February 24, meaning he could remain in jail through the Winter Olympic Games in Sochi, which end on February 23.

A request for bail or house arrest was denied.

"I love you all. I love everybody," said Russell, 59, after the judge announced her decision. "I am not a criminal," he said in comments released by Greenpeace.

Earlier in the day Russell insisted he was innocent.

"I have not committed a crime so I have nothing to run from," Russell, looking visibly upset, said from a metal cage in the courtroom.

Greenpeace International executive director Kumi Naidoo said: "This case is now a circus.

"We will continue to pursue every legal avenue we can, and leave no stone unturned, until each and every one of them is home with their families," he said.

'Let me go home'

The two courts were scheduled to rule on the detention of several more activists and freelance journalists, but some of the hearings were postponed until later this week.

The Kalininsky court was also scheduled to decide on the detention of Russian photographer Denis Sinyakov. The prosecution demanded that his extension be extended by three months, Greenpeace said on Twitter.

The Brazilian activist Maciel held several placards inside her metal cage on Monday.

"I love Russia but let me go home," read one poster. "Save the Arctic," read another.

Her lawyer earlier urged the judge to think about Russia's international reputation.

"I am calling on the court not to violate the legal norms otherwise no one would come for the Olympics because no one would want to come to a country where law is violated," Sergei Golubok said in court.

But Nikolai Petrov, an analyst with the Higher School of Economics, suggested the activists could be released in the run-up to the high-profile event "to improve Russia's image".

The countries were put in pre-trial jail in September after their ship was seized at gunpoint by Russian security forces following their open-sea protest against Arctic oil drilling.

A range of stars including Madonna and politicians such as German Chancellor Angela Merkel have called for the crew's release.

The global outcry over the Greenpeace campaigners' treatment has been compared to the international shock following the jailing for two years of two members of the punk band Pussy Riot after they performed an anti-Putin song in a Moscow cathedral last year.

On Friday, an international maritime court will rule whether to order Russia to release the activists in a case brought by the Netherlands, the ship's flag country.