The Russian Coast Guard disrupted an attempt by the activists on Sept. 18 to scale the Russian Arctic platform. Russian authorities seized Greenpeace's ship, the Arctic Sunrise, the next day and towed it with the 30 people aboard to Murmansk.
No charges have been brought against anyone in the group, and several activists' cases are still being considered by the court. Judges have been deciding whether to jail each of those who were on board the ship pending the investigation. Russian authorities are looking into whether they could be charged with piracy, among other offences.
The court on Thursday denied bail and sanctioned a two-month jail term for Russian photographer Denis Sinyakov and Greenpeace spokesman Roman Dolgov, also from Russia.
It handed out similar terms to the ship captain, Pete Willcox of the United States; Canadian crew member Paul Douglas Ruzycki; boat mechanic Jonathan Beauchamp of New Zealand; Francesco Pisanu of France; Gizhem Akhan of Turkey and Marco Weber from Switzerland, among others. Several other activists were jailed only for three days pending the probe.
Ruzycki, of Port Colborne, Ont., was serving as the ship's chief mate when it was seized last Thursday. Montrealer Alexandre Paul, 35, was also on board.
Paul's mother, Nicole Paul, expressed concern Thursday about her son's plight.
''Let's just say it's not easy,'' she told The Canadian Press. ''Things are getting down to the nitty-gritty.
''Where is it all going to end? We don't know what the (detention) conditions are. We're told they're together, fine, but that's not that reassuring. Russia is another reality.''
She urged the federal government to get more involved.
''They were there to defend the environment and, as far as I know, there was no violence. My husband and I are helpless.''
Russia's Investigative Committee spokesman Vladimir Markin said some of those jailed could be released before two months are up as investigators clarify what roles they played in the protest.
Although Russian President Vladimir Putin said Wednesday the activists aren't pirates, he defended their detention.
The detained activists are from 18 countries, including Russia, and a long detention or trials could draw unwelcome international attention to Russia's tough policy against protests.
Greenpeace's executive director, Kumi Naidoo, said in an emailed statement that "the Russian authorities are trying to scare people who stand up to the oil industry in the Arctic, but this blatant intimidation will not succeed."
Reporters Without Borders said it was appalled by the jailing of the Russian photographer, Sinyakov, saying his arrest was "an unacceptable violation of freedom of information." The top trans-Atlantic security and rights group, the Organization for Security and Cooperation in Europe, also voiced concern and demanded Sinyakov's immediate release.
"It is worrisome that Sinyakov was arrested while performing his professional duties as a photojournalist," Dunja Mijatovic, the OSCE's media freedom representative, wrote in a letter to the Russian Investigative Committee chief.
Sinyakov is a contributor to various international and Russian media outlets. Several Russian online media outlets said they would take all pictures off their websites in a show of solidarity with Sinyakov.
The platform, which belongs to an oil subsidiary of the state gas company Gazprom, is the first offshore rig in the Arctic. It was deployed to the vast Prirazlomnoye oil field in the Pechora Sea in 2011, but its launch has been delayed by technological challenges. Gazprom said earlier this month it was to start pumping oil this year, but no precise date has been set.
The Arctic Sunrise sails under the Dutch flag. The Netherlands has asked Russia to release the ship and its crew immediately, explain the legal basis for its actions and any charges against the activists.
Vasilyeva reported from Moscow. Vladimir Isachenkov in Moscow contributed to this report. Also with files from Melanie Marquis of The Canadian Press in Montreal