MOSCOW -- Russia's Federal Security Service announced on Friday that it had seized a Greenpeace International ship and its crew after a series of protests at an offshore oil rig in the Arctic Ocean and that it would tow the ship to port in Murmansk to conduct an investigation.
The seizure of the ship on Thursday night, which was carried out by armed border guards dropped by helicopter, threatened to escalate into a diplomatic confrontation, since the crew includes citizens of several countries, including one American. Russia's Ministry of Foreign Affairs had already issued a protest to the Dutch ambassador, because the ship, the Arctic Sunrise, is registered in the Netherlands and Greenpeace International is based there.
The Federal Security Service, which oversees Russia's border guards, said in a statement that the ship had been seized under laws governing Russia's exclusive economic zone and that its activities would be reported to the country's Investigative Committee for possible criminal charges. The committee's regional branch, in a separate statement, said it was considering charges of piracy.
The ship was seized in international waters near the Prirazlomnaya platform in the Pechora Sea, not far from the island of Novaya Zemlya. The platform, owned by the state-controlled energy giant Gazprom, is the first offshore oil rig in the Arctic. It was completed last year and is expected to begin pumping oil next spring. Greenpeace had sent its ship to the area last month to protest what it considers to be the risks of drilling for oil in such an environmentally fragile and largely unspoiled region.
On Wednesday, two of the ship's activists managed to scale the rig and were detained, prompting the initial Russian diplomatic protests. The border troops had also fired several warning shots during protests, but no one was injured during the storming of the ship on Thursday night, according to the security service and Greenpeace. Even so, the head of the organization's Arctic oil campaign, Ben Ayliffe, said the seizure was unprecedented.
"We have no idea why they're being held," he said of the ship's crew. "Are they being charged? Why were they detaining our ship in international waters?"
The security service said there were 27 people on board, including 4 Russians. Greenpeace said the crew totaled 30. The reason for the discrepancy was not immediately clear.
Greenpeace officials in Moscow, who have monitored the ship's activities from a "war room" in the organization's office, said there had been no contact with the crew since Thursday night and no official response from the authorities beyond the security service's statement on Friday, confirming the seizure. According to Greenpeace, at its current speed under tow, the ship will arrive in Murmansk on Monday.
Before communications were severed, the activists had reported that the troops who boarded the ship had "behaved quite correctly, but bureaucratically, the Soviet way," said Vladimir Chuprov, a leader of Greenpeace Russia.
In its statement, the security service, known by the initials F.S.B., said a search of the ship uncovered "a large collection" of photographic and video equipment and small boats, suggesting unauthorized activity against Russia's national security, though it did not explain the significance of the discovery.
"What the F.S.B. is doing now is not to protect the national interest," Mr. Chuprov said in an interview in the organization's Moscow office. Instead, he added, referring to major energy companies now exploring the possibility of an energy boom in the Arctic, "The threat to the national interest is in the offices of Gazprom, Rosneft, Shell, BP or whatever."
This article originally appeared in The New York Times.