Joseph Kabila was sworn in Tuesday for a new term as president of Democratic Republic of Congo following his victory in a disputed election, promising to improve the business climate and rebuild infrastructure.

The ceremony, clouded by an opposition rejection of Kabila's win in the November 28 poll, was held in a heavily guarded compound on the banks of the Congo River in the capital Kinshasa and was attended by only one foreign head of state, Zimbabwe President Robert Mugabe.

Ambassadors from the United States, France and the United Kingdom were also there.

We are going to pursue an improvement of the business climate to better serve investors. We are also going to pursue and accelerate the reconstruction of the country, Kabila told a few thousand supporters after he was sworn in by the Supreme Court.

Kabila, in power since his father's assassination in 2001, was reelected in a November 28 poll meant to shore up stability in the central African state, but which was instead marred by deadly violence and allegations of fraud.

Top opposition figure Etienne Tshisekedi has rejected Kabila's reelection, and declared himself president, raising fears of renewed street violence in the Kinshasa where he is popular. He is planning his own inauguration Friday.

Normally bustling Kinshasa was mostly quiet Tuesday, with riot wagons and security forces cruising through the streets.

Human rights group Amnesty International said late Monday that Congolese security forces had been rounding up opposition supporters since the election, and called for the arrests to stop and detainees to be released.

Speaking after his inauguration, Kabila said that the electoral process represented the first time in Congo's history that a presidential mandate had ended without a crisis, and praised Congolese for their discipline.

You were asked to choose on the one hand between an illusory promise based on incendiary language, and on the other hand the consolidation of peace and stability, he said.

The November 28 poll marked the second presidential contest since a 1998-2003 war that killed more than 5 million people, and was seen as key to cementing gains in a country that lies on the bottom of the U.N. index for human development - a measure of average wealth, education and life expectancy.

Congo is the sixth worst place to do business out of 183 countries ranked by the World Bank, despite its vast mineral resources, and the average person lives on just over 50 cents a day. Congo's government has also struggled to put an end to simmering rebellions in Congo's eastern provinces, despite U.N. backing.

(Additional reporting and Editing by Richard Valdmanis)