( CNN ) -- Sweden 's capital endured a fourth consecutive night of rioting Wednesday , with fires and clashes with authorities decreasing in the original flashpoint in the northern suburbs but increasing to the south , police said . Rioters continued to set fires to vehicles and other structures in Stockholm and suburbs , and they pelted responding firefighters and police with rocks and other objects , Stockholm police press officer Kjell Lindgren said Thursday . Early media reports said the four days of riots , which started in the high-unemployment , low-income northern suburb of Husby on Sunday , might have been triggered by last week 's shooting death of a man by police . But police said Wednesday they were not sure of the cause . Among Wednesday 's incidents : Rioters set fire to a restaurant and tried to burn two police stations , Lindgren said . The fires at the police stations were extinguished before the stations were destroyed . `` In the southern parts of our city ... we 've seen an increase in violence , and most of our police officers and firemen who were working overnight have said that this has been very difficult , with so many incidents in so many places , '' Lindgren said . He said 10 fires were set in the northern Stockholm area overnight , but he did n't have a number for the southern suburbs . The Local , an English-language online newspaper , reported that Stockholm 's fire service had responded to at least 75 incidents throughout the city by 2 a.m. Thursday . Police were so busy escorting firefighters , `` we 've only had time to arrest one person '' overnight -- a 16-year-old girl on suspicion of preparing arson , Lindgren said . Eight people were arrested in Husby on Tuesday night , according to police . More than 100 vehicles were set on fire Sunday night just in Husby , police said . Another 29 were set on fire Tuesday night in the wider district , they said . Husby is an area that has a lot of problems and a high crime rate , according to Lindgren . Tensions have been brewing since May 13 , when police shot dead a 69-year-old Husby man who had a machete , The Local newspaper said . On Wednesday , Stockholm police spokesman Lars Bystrom told CNN that authorities were n't sure why the riots began . `` We have ... heard the reports that some are making the connection to the 69-year-old man who was shot dead by police this past Monday on May 13 in his apartment after he threatened police with a machete , and the officers attending felt their life was in danger and had to react , '' Bystrom said . `` But we do n't know for sure what is actually behind this . At this point , it is pure speculation . `` It would be very unfortunate if we started hesitating to go in when serious incidents happen because of this . '' The Local also quoted a local youth leader as saying some police officers used racial slurs against residents Sunday as the trouble flared . Bystrom said Wednesday that police are investigating `` possible use of inappropriate language or excessive use of force . '' The disorder led Swedish Prime Minister Fredrik Reinfeldt to issue a statement Tuesday appealing for calm . `` We have had two nights of great worry , damage to property and a threatening mood in Husby . There is a risk that it will continue . Now everyone must help out to calm things down , '' he said . `` We have groups of young men who believe one should and can change our society through violence . We can not let violence govern . '' Reinfeldt said the trouble reflects a broader problem in Swedish society : More should be done to support education and help young people into work , he said . CNN 's Jason Hanna , Stephanie Halasz and Laura Smith-Spark contributed to this report .
Stockholm : People set fires , then pelt responding firefighters and police with stones . Husby , a northern suburb of Stockholm , had been at the center of the disorder . But police say violence is increasing in the southern suburbs . Prime Minister Fredrik Reinfeldt has appealed for calm in the capital .