SALEKHARD, Russia -- President Vladimir V. Putin said on Wednesday that the Russian authorities were justified in seizing a Greenpeace International ship at an offshore oil platform in the Arctic last week, but he questioned whether the activities of the ship's 30 crew members warranted the piracy charges that Russian authorities said they would pursue.
"I don't know the details of what happened there," Mr. Putin said here at an international conference on the Arctic, "but obviously they are not pirates. However, formally, they tried to seize our platform."
The ship, the Arctic Sunrise, was towed into the port of Murmansk on Tuesday, five days after armed border guards descended from helicopters and took control of it. The crew, which includes an American captain, Peter Willcox, and citizens of 17 other countries, is being detained and questioned in Murmansk, Russian officials said. By Wednesday evening, all crew members had been questioned by investigators, according to Greenpeace, and diplomats from several countries had been to see the crew.
Mr. Putin appeared intent on defusing potential diplomatic tensions over the episode. He said Greenpeace had clearly violated international law by sending activists from the ship in inflatable boats to try to board the Prirazlomnaya oil platform in the Pechora Sea.
Though the ship was distinctly painted with Greenpeace's logo, Mr. Putin said that Russian security officials could not be sure of the activists' identity or intentions.
"Our border guards did not know who was trying to seize our platform under the disguise of Greenpeace," Mr. Putin said. Referring to the deadly terrorist attack on the shopping mall in Nairobi, Kenya, which began after the Arctic Sunrise was already in tow, Mr. Putin added, "Especially, in the context of the bloody events that took place in Kenya, anything might have happened."
Kumi Naidoo, the executive director of Greenpeace International, said that the ship was clearly marked and that the activists were engaged solely in peaceful protest, citing as evidence a video of the incident recorded by Russian law enforcement officials and released on YouTube.
"We welcome President Putin's recognition that our activists are clearly not pirates, and acted purely out of concern for the Arctic environment," Mr. Naidoo said in a statement. "Our climbers attempted to attach themselves to the side of the platform to raise attention to the threat of Arctic oil drilling in this fragile environment and the urgent need to deal with climate change."
Under Russian law, investigators must either charge or release the activists within 48 hours. A Greenpeace representative in Murmansk said on Wednesday that none had been charged yet. Several prominent international organizations, including the World Wildlife Fund and Amnesty International, have called on Russia to release them.
The Foreign Ministry of the Netherlands on Wednesday demanded that Russia release the ship, which was flying under a Dutch flag, and the crew, which includes several Dutch citizens.
The seizure of the Arctic Sunrise has focused new attention on Russia's ambitions to develop the Arctic as climate change makes the region more accessible for larger parts of the year. It also cast a shadow over the international conference, where Mr. Putin, joined by the presidents of Finland and Iceland and scores of diplomats, scientists and oil executives, pledged to foster diplomatic, economic and environmental cooperation in the Arctic.
"We are not shying away from it," Mr. Putin said of the debate over the impact of economic development in the Arctic. "We are gathered at such events to discuss all these problems."
At the same time, he made it clear that Russia intended to exploit the resources in the region. "From time immemorial, mankind used nature to satisfy its needs, more and more," Mr. Putin said. "First it was mushroom picking and animal hunting, later on it was mineral resources, metals, hydrocarbons. Can it be stopped? Of course not. It's impossible to stop. The question is how to use them sustainably, how to minimize the damage to nature or to bring it to zero."
Steven Lee Myers reported from Salekhard, Russia, and Andrew Roth reported from Moscow.
This article originally appeared in The New York Times.