A Russian court on Thursday put a photographer and several Greenpeace activists under arrest for staging a protest at Russia’s first Arctic oil drilling site that had broken international law.

The activists attempted to scale the Russian Artic platform on Sept. 18, but were stopped by the Coast Guard, Reuters reports. Investigators are looking into charges of piracy, which is punishable by up to 15 years in prison.

President Vladimir Putin made clear that he did not believe the activists were pirates, but that “law enforcement institutions [and] border guards didn't know who was trying to seize this platform under the guise of Greenpeace,” and that while activists may not be guilty of piracy, they did break international law in their attempt to climb the oil platform.

According to Greenpeace, freelance photographer Denis Sinyakov and Greenpeace spokesperson Roman Dolgov as well as five other activists have been detained for 2 months pending piracy investigation. Greenpeace international spokesperson Dima Litvitnov has also been detained.

The environmental activist group has previously stated that an Artic oil spill is inevitable if Russia proceeds with drilling. Greenpeace warned that the platform itself, Prirazlomnaya, is no example of modern engineering—in fact, the materials used to build it are quite old and have suffered from disuse. Additionally, several sources have noted that the platform is barely 50% ready for use, and may not even meet Russian offshore operating standards.