Slovenian activities hung photos of their detained colleagues in Ljubljana's Prešeren Square and collected signatures for their release.

"28 activists and two journalists are detained after staging a protest against Arctic oil drilling on a Gazprom oil platform. Today's solidarity event is organised to urge their immediate release so they can return to their families," Dejan Savić of Greenpeace Slovenia told the STA.

Similar actions are taking place in as many as 47 countries around the world.

The campaign comes after a Greenpeace ship was impounded by Russian authorities last month after it approached the world's first oil rig in the northern Barents Sea. The international crew have been charged with piracy and could face jail terms of between 10 and 15 years.

According to Savič, the actions of Russian authorities are "illegal". Greenpeace Slovenia there welcomes the decision of the Netherlands to take legal action to protect the activists who sailed under a Dutch flag, he added.