Protest groups filed suit with a German court Monday seeking to overturn the authorities' ban on demonstrations at an airport where officials are to arrive for next month's G8 summit. Tension has risen in Germany since May 9 police raids on leftists aiming to disrupt the summit. Radicals rioted the same day and have cried foul at a ban on protests within 200 metres of a perimeter fence around the summit. Work was proceeding Monday on a 3.5-kilometre marine net to keep boats away from the Baltic coast resort of Heiligendamm, which already has a 12-kilometre welded-mesh fence round it on the land side. Sources told Deutsche Presse-Agentur dpa there would be more than 50 boats and 500 seaborne police on duty at the summit. Germany's Left Party said Monday it would officially support the protests during the June 6-8 summit. The party said the summit was unnecessary and all issues should be debated at the United Nations instead. Leaders of the Group of Seven (G7) nations and Russia meet every year to discuss economic and other issues. Anti-globalization activists demanded an urgent injunction allowing protests at Rostock Airport, the nearest airport, where world leaders are expected to land and transfer to helicopters to reach the summit venue. A similar lawsuit against the buffer zone around Heiligendamm was filed Friday. Far-left militants have mounted attacks on property in Hamburg and Berlin in recent months. All 14 petrol-bombings and five attacks with paint-bombs and stones on buildings and cars have been under cover of night. Nobody has been hurt. Police have made no arrests.