Maputo - Mozambique's new President Filipe Nyusi was sworn into office on Thursday in a ceremony boycotted by the main opposition party, which has rejected the results of October's elections.Nyusi's inauguration extended the ruling Frelimo party's nearly 40-year hold on power since the southern African nation won independence from Portugal in 1975."This takeover of power is illegal," Renamo leader Afonso Dhlakama was quoted by Lusa news agency as saying ahead of the ceremony, which was attended by regional leaders and Portuguese President Anibal Cavaco Silva.Dhlakama, a former rebel leader who claims the elections were fraudulent, boycotted the opening of parliament on Monday and has threatened to form a parallel government in parts of the gas-rich country.Nyusi, 55, took the oath of office before symbolically exchanging seats with outgoing president Armando Guebuza.He pledged "to open constructive dialogue with all political forces and civil society organisations to promote peace" in a country that was ravaged by a brutal 16-year civil war that ended in 1992."I represent a new generation, a generation that inherits huge success and exciting challenges," he said. The former defence minister is Mozambique's first president not to have fought in the liberation war against colonial power Portugal and holds no top position in the nominally Marxist-Leninist Frelimo party.An engineer by profession, Nyusi took 57% of the vote in the election - a sharp drop on the 75% of votes won by Guebuza in the previous presidential election in 2009.Growing economyHe inherits a growing economy with massive potential, but whose recent gas and oil finds have yet to benefit the impoverished majority in a country plagued by inequality and unemployment."Reforming the agricultural sector will be one of the main challenges for the new president because it comprises 70% of the jobs in Mozambique," said economist Joao Mosca.Nyusi's immediate focus, however, will be stabilising the volatile political situation given Renamo's defiant stance on the election results.Dhlakama has a habit of challenging election results. He has disputed the outcome of every election since 1990, and in the months leading up to the October poll led a low-level insurgency against the government from his bush hideout.The difference this time is his resurgent popularity, says Fernando Lima, director of Savana independent weekly - particularly in the under-developed central and northern parts of the country.Good ideasDhlakama took 37% of the vote, more than double his 2009 score of 16%."Without forming a unity government, I think Frelimo could still be generous and give governorships or agree with Renamo on ministerial positions," said Lima.How Nyusi chooses to compose his first government will give an indication of how he intends to deal with Renamo."I will be open to propositions and ideas from other other parties that promote the peace and development of Mozambique," he said at his inauguration. "Good ideas do not wear party colours."The leaders of South Africa, Lesotho, Namibia and Tanzania also attended the swearing-in ceremony at Independence Square in the seaside capital Maputo.