NAIROBI (Reuters) - Tanzania’s President John Magufuli has promised to work with his rivals after a landslide victory in an election that his leading opponent described as a travesty and the United States said was marred by widespread irregularities.The overture comes ahead of demonstrations the opposition has called for on Monday to protest against the poll’s results. “I will be the servant of all Tanzanians. I would like to thank my fellow presidential contestants for participating,” Magufuli said at a function in the capital Dodoma where he formally accepted the results. According to results announced by the country’s poll body on Friday, Magufuli secured 84% of the vote against his leading opponent Tindu Lissu’s 13%. “I promise to work with you to ensure we are pushing for the national development. Development is non-partisan ... politics is not a war, politics is not a conflict, we are all Tanzanians.”