Dutch police on Tuesday arrested six activists as Greenpeace staged two protests in northern Europe including chaining a Russian contracted oil rig to a dock, to highlight oil drilling in the eco-sensitive Arctic oceans.

"Police have arrested six of our activists. They are still in custody but we don't know what the charges are," said Faiza Oulahsen, who coordinated the protest in the northwestern Dutch port of IJmuiden.

In Norway, 15 Greenpeace activists boarded the Barents Sea oil rig, the Transocean Spitsbergen, which is due to drill the Scandinavian country's northernmost well, another Greenpeace spokesman said.

The activists were still on board the Spitsbergen, with Greenpeace's Juha Aromaa telling AFP the activists had food and supplies "to stay on board for several days."

Dutch police spokesman Koos Venema confirmed the arrests in IJmuiden, saying the activists were detained after refusing a police order to abandon the GSP Saturn platform, anchored in the port city northwest of Amsterdam.

Greenpeace divers and activists with climbing gear late Monday night surrounded the massive Saturn platform, which has been contracted by Russian state oil giant Gazprom to drill for oil in the northern Pechora Sea.

"The divers chained the rig to the quay to prevent it from leaving the harbour," Greenpeace said in a statement.

"The activists wanted to prevent the Saturn... from going to the Dolginskoye field to drill for oil for Gazprom," it added.

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, which has a crew of 100, is the second to be targeted by Greenpeace's campaign to highlight the dangers of oil drilling in the eco-sensitive North Pole area.

Russian security forces in September detained 30 Greenpeace activists and journalists and seized their Arctic Sunrise ship over the protest at an another offshore oil rig owned by Gazprom.

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.

"We will continue to campaign against Shell and Gazprom which want to use climate change to drill for oil in the vulnerable North Pole area," said Olahsen, who is one of the so-called "Arctic 30" activists arrested in Russia.

Both Gazprom and the largely Norwegian state-owned Statoil reacted with anger on Tuesday.

"Today, some thugs mounted the platform and deployed placards, but the platform has left the port and is following its planned route," Gazprom spokesman Sergei Kupriyanov told Moscow's Radio Echo.

Statoil accused Greenpeace of behaving "irresponsibly and illegally."

"Statoil respects the right for legal protests and believes it is important with a democratic debate on the oil and industry," the company said in a statement.

But "the safety of people and the environment is the first priority, and we do not want activity that can increase the risk level."

"When they still use this form of protest we believe they act irresponsibly and illegally," Statoil said.

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