The Democratic Republic of Congo's President, Joseph Kabila, has been sworn in for a second term in Kinshasa. He reportedly promised to safeguard national unity, as tanks were deployed in the capital to prevent protests. Mr Kabila's inauguration went ahead after the country's Supreme Court upheld his victory in November's disputed presidential election. Opposition leader Etienne Tshisekedi maintains he won the poll and says he will swear himself in on Friday. The elections were the first to be organised locally since the end of a devastating civil war in 2003, which left some four million people dead. The BBC's Thomas Hubert in Kinshasa says Mr Kabila, 40, took the oath of office in the presidential compound, in the presence of a few thousand supporters. Our reporter says a 21-gun salute echoed around the empty streets of the capital as President Kabila took his oath in front of the Supreme Court and received symbols of power from traditional chiefs such as wooden statues and a leopard's skin. The government declared a public holiday for the inauguration, while the opposition called for strikes in Kinshasa and other cities. Belgian boycott Zimbabwe's Robert Mugabe was the only foreign head of state present - our reporter says this is a sign of the discomfort generated by widespread irregularities in Mr Kabila's re-election. Mr Mugabe sent troops to back Mr Kabila's father, Laurent, during the conflict in DR Congo. All ambassadors in the country were summoned to attend the inauguration or risk being made persona non grata. Taking his oath of office, Mr Kabila pledged to allow himself to be guided only by the general interest, "the respect of human rights to concentrate all my efforts to promote our common well-being and peace". DR Congo is two-thirds the size of Western Europe and is rich in minerals, but it has hardly any roads or railways. After years of mismanagement and conflict, living standards in the country were recently found to be the lowest of 187 countries surveyed by the UN. In his speech, Mr Kabila promised: to create more jobs; build more hospitals and health centres; reduce reliance on the mining sector; revise the mining code; boost agricultural production ; improve DR Congo's self-reliance by "rejecting our country's status as the world's supermarket". Our reporter says the mention of revising the mining code is unlikely to go down well in the West. The foreign minister of former colonial power Belgium cancelled plans to attend the ceremony. Congolese affairs analyst Theodore Trefon says that Western nations often follow Belgium's diplomatic lead over DR Congo. Regional powerhouse South Africa said it would send its Foreign Minister, Maite Nkoana-Mashabane, after describing the elections as "generally OK". Along with the opposition, local and international electoral observers denounced widespread irregularities in November's presidential poll. Mr Tshisekedi, 79, who enjoys strong support in Kinshasa, has called on civil servants and the security forces to take orders from him, rather than Mr Kabila. He has also said he is offering a reward for the capture of Mr Kabila. An aide of Mr Kabila said the move was "criminal". Mr Tshisekedi led the campaign for democracy under former leader Mobutu Sese Seko, but these were the first elections he has contested. He boycotted the last poll in 2006, organised under the auspices of the United Nations, after claiming they had been rigged in advance. As well as Kinshasa, Mr Tshisekedi enjoys a lot of support in the diamond-rich, central area of Kasai. Mr Kabila has been president since 2001 following the assassination of his father. Last week, Mr Kabila admitted there had been mistakes in the electoral process, but said no poll was 100% perfect and he rejected concerns that the results lacked credibility. The US-based Carter Center, which sent observers to the election, said the vote was too flawed to be credible. The US state department called for a review of irregularities and the EU described parts of the election process as "chaotic". However, the African Union described the elections as a success.