* Kabila congratulates Congolese voters
* Mugabe, Western ambassadors attend ceremony
* Amnesty International calls for halt to opposition arrests
By Jonny Hogg
KINSHASA, Dec 20 (Reuters) - Joseph Kabila was swornin on Tuesday for a new term as president of Democratic Republicof Congo, promising to improve the business climate and rebuildinfrastructure destroyed during decades of conflict.
Kabila, in power in the central African state since hisfather's assassination in 2001, was reelected in a Nov. 28 pollmeant to shore up stability, but which was marred by deadlyviolence and allegations of fraud.
"We are going to pursue an improvement of the businessclimate to better serve investors. We are also going to pursueand accelerate the reconstruction of the country," Kabila saidafter he was sworn in by the Supreme Court.
He said reconstruction would focus on communicationinfrastructure in the vast country, which is over half the sizeof the European Union, but would also include projects such asbuilding hospitals and schools.
Congo is the sixth worst place to do business out of 183countries ranked by the World Bank, despite its vast mineralsresources, and the average person lives on just over 50 cents aday.
Zimbabwe President Robert Mugabe attended the inaugurationheld by the banks of the Congo River, along with ministers ofother African countries and ambassadors from the United States,France and Britain.
Speaking after his swearing-in, Kabila said that theelectoral process represented the first time in Congo's historythat a presidential mandate had ended without a crisis, andpraised Congolese for their discipline.
"You were asked to choose on the one hand between anillusory promise based on incendiary language, and on the otherhand the consolidation of peace and stability," Kabila saidafter being sworn in by the Supreme Court.
The Nov. 28 poll marked the second presidential contestsince a 1998-2003 war that killed more than 5 million people,and was seen as key to cementing gains in a country that lies onthe bottom of the U.N. index for human development - a measureof average wealth, education and life expectancy.
But the vote was marred by lethal clashes between oppositionsupporters and security forces, allegations of rigging, andcriticism from observer missions over poll irregularities.
Top opposition figure Etienne Tshisekedi rejected theresults handing Kabila reelection, and declared himselfpresident, raising fears of renewed street violence in thecapital Kinshasa where he is popular.
Human rights group Amnesty International said late on Mondaythat Congolese security forces had been rounding up oppositionsupporters since the election, and called for the arrests tostop and detainees to be released.
Kabila came to power after his father, Laurent, wasassassinated in 2001, and he later won election in 2006, inpolls set by the United Nations.
Kabila has struggled to put an end to simmering rebellionsin Congo's eastern provinces, despite U.N. backing, andinvestors say the country remains one of the most challenging inthe world for businesses despite its vast minerals riches. (Additional reporting and Editing by Richard Valdmanis)