At least 20 people, including one policeman, have been killed in riots in the Nigerian city of Jos after local elections, aid workers say. A local journalist told the BBC that Muslim opposition supporters had gone on the rampage when they heard their candidate to head the council had lost. This sparked unrest in the religiously divided city, with Christians burning mosques and Muslims burning churches. A dusk-to-dawn curfew has been imposed and the army sent to restore order. In 2001, more than 1,000 people died in religious clashes in the city. An unnamed Red Cross worker told Reuters news agency that at least 20 people had been killed and 300 wounded in the clashes. "Very early this morning a group of protesters macheted to death a policeman," one witness told Reuters. A police spokesman confirmed to the BBC that one officer had died but could not give an exact number of civilians casualties. Poll rumours A lecturer at the University of Jos said smoke could be seen from burning tires and buildings. "From where I'm standing I can see smoke coming from all over the city," Victor Dugga told the BBC's Focus on Africa programme. He added that people are very worried as there has been no information on the local media about the violence. "We have three radio stations in Jos and they are only playing music and telling us about what happened yesterday. Nobody is telling us what happened now," he said. The protests started overnight with singing and burning of tyres on the roads by groups of youths over reports of election rigging. The election result has not been officially announced but the protests turned violent after a rumour spread that the opposition candidate to lead the local council had been defeated. The opposition All Nigeria People's Party and the ruling People's Democratic Party allegedly involved in the fray are yet to make any statement on the matter. Local journalist Senan Murray told the BBC's Hausa Service that Muslims in the city tend to support the ANPP and Christians the PDP. In 2004, a state of emergency was declared in Plateau State, of which Jos is the capital, after more than 200 Muslims were killed in the town of Yelwa in attacks by Christian militia. Correspondents say communal violence in Nigeria is complex, but it often boils down to competition for resources such as land between those that see themselves as the true "indigenes" of an area, and those that are considered to be more recent "settlers". In Plateau State, Christians are regarded as the indigenes and Hausa-speaking Muslims the settlers. Source: BBC