The German branch of the environmental lobby group said in a statement posted on its website that demonstrations were planned in 30 cities in Germany on Saturday to demand that Russia free the 28 activists and two journalists, who have been held in custody for more than a fortnight.
A statement on the group's international page described those being held as the "Arctic 30," and called on supporters to take part in an "emergency global day of solidarity events" this Saturday.
The activists, who include citizens of a number of countries, were taken into custody last month after several of them scaled an oil platform owned by energy giant Gazprom in the Barents Sea to protest against Russia's plans to drill in the Arctic.
Russian border guards subsequently lowered themselves onto the Greenpeace icebreaker Arctic Sunrise from a helicopter and arrested all on board. The Arctic Sunrise was then towed to the Russian port of Murmansk, where a court charged the crew members with piracy.
Saturday's protests, which began with Greenpeace supporters forming a human chain in Hong Kong, were just the latest effort to apply pressure on Russian authorities to free the activists, who could face maximum prison sentences of 15 years.
The rallies come a day after the Netherlands announced that it was launching legal proceedings against Russia, arguing that the arrests and seizure of the vessel, which was sailing under a Dutch flag, were unlawful.
"The Netherlands... today started an arbitration process on the basis of the UN Convention of the Law of the Sea," the Dutch foreign minister, Frans Timmermans, said in a letter to parliament on Friday.
The move was welcomed by Greenpeace, which has said those being held include two Britons, two Canadians, two Russians, two New Zealanders, as well as citizens of the United States, Australia, France, Denmark, Italy, Switzerland and Turkey.
"Russian officials will now be called to explain their actions before an international court of law, where (they) will be unable to justify these absurd piracy allegations," the AFP news agency quoted Greenpeace lawyer Jasper Teulings as saying.
On Saturday, though, Russia defended the arrests, saying Greenpeace had been given sufficient warning about what would happen if its activists approached the oil platform.
"Everything that happened with the Arctic Sunrise is a pure provocation," Deputy Foreign Minister Alexei Meshkov told the Russian news agency RIA Novosti.
pfd/tj (AFP, Reuters)