Greenpeace said 30 activists boarded a rig contracted by Russian energy company Gazprom for work in the northern Pechora Sea. They were there for five hours and six of them were arrested by Dutch authorities.
Another group of 15 demonstrators is on board a rig contracted by Norwegian energy company Statoil for work in the northern reaches of the Barents Sea.
Greenpeace International campaigner Ben Ayliffe said energy companies working to tap into frontier arctic basins are behaving recklessly.
"We cannot let a reckless club of international oil companies hunt for the last drops as the ice melts away," he said in a statement Tuesday.
Changes in the global climate mean parts of the arctic are free from ice for longer periods, giving energy companies more time to explore undeveloped resources in the region. Groups like Greenpeace worry the work could harm the pristine arctic environment.
Greenpeace activists, dubbed the Arctic 30, were arrested for a similar demonstration targeting Gazprom last year.
Statoil said in a statement it wouldn't drill into oil reserves of the targeted Hoop area in the Barents Sea until a complaint from Greenpeace has been assessed by the Norwegian Ministry of Climate and Environment.
Gazprom officials told state news agency RIA Novosti it's work plan was unaffected by the actions from Greenpeace.