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.