"In my hands, I have the documents that confirm that 10 have already been remanded in custody for two months. They're citizens of Russia, France, Turkey, Poland, Sweden, Canada and New Zealand," said Greenpeace Russia's Anton Beneslavski.
The US citizen who skippered the Arctic Sunrise icebreaker was among those remanded, other sources said.
The court must still decide whether the remaining activists will be released or held pending a piracy investigation.
All 30 could face formal charges of piracy for their September 18 protest in the Pechora Sea, although Russian President Vladimir Putin said this week that the activists are not pirates.
After several of the Greenpeace members tried to board a drilling platform operated by Russian state energy titan Gazprom, the Arctic Sunrise was seized last Thursday by the Russian coast guard and its crew members were detained.
"We have sufficient legal basis for appealing all the actions taken by the Russian authorities in this process," Beneslavski said.
Russia is facing international calls to release activists
"Violence was not employed during the protest. There was no assault nor illegal seizure of another's property, and also no attempt to take control of the (platform)," Greenpeace Russia said.
Meanwhile, Russia is facing international calls to release the activists, with the Netherlands, where the environmental watchdog is based, saying it was not ruling out resorting to other legal avenues if Moscow does not respond promptly to its request.
Gazprom claims the Greenpeace action endangered the health and lives of workers on the Prirazlomnaya oil platform. Greenpeace says Gazprom's plans to begin oil production with that platform in the first quarter of 2014 increase the risk of an oil spill in an area that contains three natural reserves protected by Russian law.