(Adds quotes from ceremony, SLPP offices looted, man killed) By Katrina Manson and Christo Johnson FREETOWN, Sept 17 (Reuters) - Opposition leader Ernest Bai Koroma was sworn in as Sierra Leone's president on Monday after winning polls marked by violence and some fraud, prompting celebrations and looting in which at least one man was killed. The 53-year-old former insurance executive, who came second in a 2002 poll, took his oath before the chief justice at State House in the war-scarred West African state's capital Freetown. The National Electoral Commission (NEC) earlier declared the All People's Congress (APC) candidate the winner of the Sept. 8 poll, despite a threat by the ruling Sierra Leone People's Party (SLPP) to challenge the result in court. "Let us view this not as a victory for any particular group or political party or region ... but as a victory for all Sierra Leoneans," Koroma said after swearing the oath. "Let us begin the process of healing the wounds that suddenly and unnecessarily appeared during the course of this political campaign. Let us endeavour to reconcile ourselves as one nation under God," said Koroma, a Christian from the mostly Muslim north. The NEC said Koroma had won with 54.6 percent of valid votes, defeating Vice-President Solomon Berewa, on 45.4 percent. Sporadic violence marred campaigning for the run-off, but international observers hailed the polls as an important step in the former British colony's recovery from a 1991-2002 civil war. The conflict killed 50,000 people and was marked by shocking cruelty in which civilians had limbs hacked off and children were kidnapped, drugged and forced to fight as soldiers. "It's a great moment. It sends a very strong message that it is possible to hold credible elections in Africa," Victor Angelo, head of the United Nations mission in the poor nation of 5.7 million people, told Reuters. Disgruntled SLPP officials criticised the result, but it was not immediately clear whether they would formally contest it in the Supreme Court within the required period of seven days. CHEERING, LOOTING Cheering APC supporters wearing the party's red colours blew whistles, honked car horns and danced in Freetown's streets. But some hurled stones and bottles at the SLPP headquarters, smashing windows and eventually breaking in to carry off chairs and office equipment, and police fired teargas at the crowds. Later a Reuters reporter saw a man lying dead outside. "SLPP in this country is finished," said one man nearby. Berewa and outgoing President Ahmad Tejan Kabbah pledged Koroma their support and said they were ready to work with him. The run-off poll followed an inconclusive ballot on Aug. 11, in which the APC and its allies won a parliamentary majority. The polls were the first since U.N. peacekeepers left two years ago, and many Sierra Leoneans hoped the election would help erase the bitter memories and divisions of a civil war fuelled by corruption and financed by illegal "blood diamonds". "I know how huge your expectations are. You have suffered for too long," Koroma said. "My government, a government of national unity in which nobody should feel threatened, will adopt zero tolerance on corruption." "Sierra Leone is coming from one of the most brutal wars in the world ... It's coming back to the world as a nation that can make good democratic changes," college lecturer Amos Turay said. NEC chairman Christiana Thorpe said some attempts at fraud, including stuffing and swapping ballot boxes, had been uncovered but had not affected the result. Turnout was around 68 percent.
