It is a job that will pose a challenge even to this veteran mediator.United Nation’s envoy Martti Ahtisaari has arrived in Kosovo to begin one of his toughest missions yet – tackling Europe’s biggest diplomatic predicament. The fate of the breakaway Serbian province is at stake. The former Finnish president is laying the ground for talks on whether Kosovo’s Ethnic Albanian majority wins independence, or Belgrade retains sovereignty over land it treats as the cradle of the Serb heritage. Addressing parliament today, Serbian Prime Minister Vojislav Kostunica ruled out independence, saying talks about Kosovo’s future must find a solution within the territorial integrity of Serbia. But, in views that are mutually exclusive, Kosovo’s interim government which is mainly ethnic Albanian insists independence is “non negotiable.” As he battles lung cancer, moderate Albanian President Ibrahim Rugova says he will carry on pursuing his aim of achieving independence from Serbia. Kosovo has been run by the UN since Serb forces were driven out by NATO in 1999.