RABAT (Reuters) - Morocco's "Arab Spring" protesters said they were undeterred despite a landslide victory for King Mohammed in a referendum on constitutional changes they say do nothing to ease his autocratic grip on power. Preliminary results of Friday's poll showed 98.5 percent of voters approved the text on turnout officials estimated at 73 percent. Opposition said the turnout figure looked inflated and alleged irregularities in voting procedures. The charter explicitly grants executive powers to the government but retains the king at the helm of the cabinet, army, religious authorities and the judiciary. The result followed a state media campaign in favour of the "yes" vote that appealed to a widespread sense of loyalty to the king, who is head of the Arab world's longest-serving dynasty and a staunch Western ally. The result will also be scrutinised by Gulf monarchies who have so far dodged reform calls. Western partners of Morocco urged the king to enact reforms swiftly and to listen to the demands of representatives of citizen movements. Mohammed, 47, has had some success in repairing the legacy of human right abuses, high illiteracy and poverty he inherited after his late father's 38-year rule ended in 1999. Yet critics say there remains a wide disparity between rich and poor, and complain of failings over human rights and the rule of law.