Two members of the group were detained Sept. 18 in their attempt to scale the Arctic platform. The Coast Guard seized Greenpeace's ship the next day and towed it with 30 activists aboard, to Murmansk, where they are being questioned by investigators considering piracy charges.
Putin, speaking at a forum on Arctic affairs, said that "it's completely obvious they aren't pirates." He added, however, that the officers "didn't know who was trying to seize the platform under the guise of Greenpeace.
"Especially in view of the events in Kenya, really, anything can happen," he said—referring to the deadly mall attack in Nairobi.
It was unclear whether Putin's comments might foreshadow leniency for the activists, who could face 10-15 years in prison if convicted of piracy. But Vladimir Chuprov, head of the energy department at Greenpeace Russia, welcomed the remarks as an invitation to settle the matter amicably.
"We're ready for dialogue, and I hope they will hear us," he told a news conference on Wednesday.
The detained activists are from 19 countries, including Russia, and a long detention or trials could draw unwelcome international attention to Russia's tough policy against protests.
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 their actions against the Arctic Sunrise, the exact location it was seized and any charges against the activists.
Foreign Minister Frans Timmermans said in a letter to parliament late Wednesday that he spoke to his Russian counterpart, Sergey Lavrov, about the activists' detention at United Nations headquarters in New York.
"He promised to inform us fully and to speed up the procedure so that we quickly get clarity about the ship and its crew," Timmermans wrote.
Ratcheting up the diplomatic pressure, Timmermans said the Dutch government could take legal steps including taking the dispute to the Hamburg-based International Tribunal for the Law of the Sea if it is not satisfied with the Russian response.
The platform, which belongs to an oil subsidiary of state natural 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 that it was to start pumping oil this year, but no precise date has been set.
Greenpeace insisted that under international law Russia had no right to board its ship and has no grounds to charge its activists with piracy.
"Charging us with piracy is absurd," said Ivan Blokov, campaign director at Greenpeace Russia. "Greenpeace holds non-violence as a key principle of its work and we are being charged with something that involves violence."
Chuprov denied claims that Greenpeace's ship, the Arctic Sunrise, violated the Russian three-mile security zone.
Although the Russian Coast Guard seized the ship on Thursday and has been keeping the activists captive ever since, the official 48-hour detention for them started only Tuesday night.
Blokov said no member of the crew has seen a lawyer yet and only one foreign national was able to meet with a consular official.
Jim Heintz in Moscow and Mike Corder in The Hague, Netherlands contributed to this report.