KASTELLORIZO, Greece (Reuters) - European Union president Greece challenged its partners on Saturday to consider backing the use of force as a last resort against "irresponsible nations" that build weapons of mass destruction. Greek Foreign Minister George Papandreou raised the sensitive issue on how to deal with states developing nuclear, chemical and biological weapons at a meeting of EU foreign ministers, several of whom opposed the U.S.-led war on Iraq. "Weapons of mass destruction and their proliferation are probably as historically destabilizing as the invention and spread of gunpowder," Papandreou said, according to speaking notes obtained by Reuters. "If our...