Madonna has become the latest star to call for the release of a group of Greenpeace protesters incarcerated in Russia. Twenty-eight activists for the environmental charity and two journalists were arrested in September (13) and charged on suspicion of piracy and hooliganism following a protest at sea against oil drilling in the Arctic Ocean. They are now reportedly being held at pre-trial detention centres in St Petersburg. The issue has caught the attention of several celebrities already, Beatles legend Sir Paul McCartney wrote a letter to Russian president Vladimir Putin requesting his help in freeing the activists, and French actress Marion Cotillard spent Friday (15Nov13) in a cage on the streets of Paris with fellow environmental campaigners to demand the group's release. Madonna has now joined the campaign by posting a picture on her Instagram.com page featuring the slogan, 'Free the Arctic 30'. She also posted a link to a Greenpeace petition calling for the group's release, along with the caption, "These 30 people are in prison in Russia for staging a peaceful protest in the Arctic. Let your voice be heard. Let's bring these people home." Madonna has previously thrown her support behind a campaign to free two Russian rockers from the band Pussy Riot who remain locked up in the country after performing a protest song against Putin in a Moscow church.