"Police have arrested six of our activists. They are still in custody but we don't know what the charges are," protest coordinator Faiza Oulahsen told AFP.
Police spokesman Koos Venema confirmed the arrests, saying the activists were arrested after refusing a police order to abandon the GSP Saturn platform, anchored in the Dutch port of IJmuiden, northwest of Amsterdam.
Greenpeace divers and activists with climbing gear late yesterday night surrounded the massive platform, which has been contracted by Russian state oil giant Gazprom to drill for oil in the northern Pechora Sea.
"The activists wanted to prevent the Saturn... From going to the Dolginskoye field to drill for oil for Gazprom," it added.
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Police intervened at around 0230 GMT and arrested the activists.
"They have been taken into custody and are expected to appear on charges later today of ignoring a police instruction to leave the rig," police spokesman Venema told AFP.
The Saturn rig is the second to be target by Greenpeace's campaign to highlight the dangers of oil drilling in the eco-sensitive North Pole area.
The 30, including four Russians, were detained for around two months before being bailed and then benefitting from a Kremlin-backed amnesty.
Greenpeace is now suing Russia before the European Court of Human Rights for detaining their activists.