Pete Willcox, the U.S. captain of a Greenpeace ship protesting drilling in the Arctic, is among those jailed pending a piracy investigation.

REUTERS/Igor Podgorny/Greenpeace/Handout via Reuters Greenpeace International captain Peter Willcox from the U.S. (front) is escorted at the Leninsky District Court Of Murmansk, September 26, 2013, in this handout provided by Greenpeace.

A Russian court has ordered two dozen environmental activists, including a U.S. man and a prominent freelance photographer, jailed for two months during a piracy investigation for their attempt to scale an oil rig in protest against Arctic drilling. Pete Willcox, the U.S. captain of a Greenpeace ship held by the Russian authorities last week, was among those held in custody by the Leninsky District Court in the northwest city of Murmansk on Thursday while the charges, which carry a maximum sentence of 15 years, are investigated, RIA Novosti reported. Canadian Paul Ruzycki, New Zealander David Haussmann, Frenchman Francesco Pisanu of France, Pole Tomasz Dziemianczuk, and Gizhem Akhan of Turkey were also among those denied release, as were two Russian men: Greenpeace spokesman Roman Dolgov and Denis Sinyakov, a former Reuters photographer who now works as a freelance photojournalist. Hearings were continuing late Thursday.

Stringer / Reuters Photographer Denis Sinyakov.

Prosecutors said that Sinyakov was a flight risk because he did not live in Murmansk and frequently traveled abroad. "My criminal activity is journalism, and I'm going to keep doing it," Sinyakov said. The charges have not yet been filed. The extended detention of Sinyakov prompted outrage inside the journalist community in Moscow, with reporters and photographers picketing outside the Investigative Commitee, the FBI-like agency conducting the investigation, Thursday. Photographer Mitya Aleshkovsky tweeted that several independent media outlets had agreed not to publish photographs Friday in protest, including a website for which Sinyakov was on assignment aboard the ship.

Sinyakov's wife Alina was among those protesting his arrest: Tatyana Makeyeva / Reuters

Russia is seeking to charge the activists aboard the ship Arctic Sunrise, whose members attempted to scale an oil rig owned by Russia's state-run energy giant Gazprom last week, with piracy, claiming that they were attempting to seize the platform by force. Security agencies said that oil rig personnel mistook the Greenpeace ship, which was flying under a Dutch flag, for an explosive device.

Handout / Reuters

Vladimir Markin, the Investigative Committee's spokesman, originally said that all 30 activists, who hail from 18 different countries, would be charged "regardless of their nationality," but added Thursday that the charges might be downgraded. His statement came after Russian President Vladimir Putin publicly said the activists were "obviously [...] not pirates." Putin added, however, that the activists "tried to seize our platform" and had violated international law.

Greenpeace has called the accusations "absurd," pointing to its long history of nonviolent protests and claiming that the ship was in international waters when Russian coast guard officers seized it and towed it to shore. "The Russian authorities are trying to scare people who stand up to the oil industry in the Arctic, but this blatant intimidation will not succeed," Greenpeace director Kumi Naidoo said in a statement. The activists were protesting Russia's attempts to tap potential oil and gas reserves in the Arctic made accessible by the melting of polar ice caused by global warming. Oil majors like ExxonMobil and Norway's Statoil have signed exploration deals with Russia's state-owned oil giant, Rosneft. Reporters Without Borders released a statement Thursday saying that "[if] Russia's constitutional guarantees have any meaning, neither Greenpeace's peaceful protest nor, even more so, Sinyakov's journalistic coverage of the protest constitute a crime." The Dutch foreign ministry, Amnesty International, and the World Wildlife Fund have also called for Russia to release the activists. Nearly 500,000 people have signed a Greenpeace petition asking Russia to drop the charges and stop drilling for oil in the Arctic.