Student protesters pelted 20 police stations with rocks and bottles, overturned cars and blocked streets in central Athens on Thursday. Police responded with tear gas as sporadic violence persisted amid Greece's worst rioting in decades. Four people were detained and at least one man was hospitalized with injuries, authorities said. Lawmakers in parliament, meanwhile, held a minute of silence for the 15-year-old boy whose shooting death by police ignited the uproar on the streets. At least 70 people have been injured and about 100 arrested since Saturday, when the rioting broke out within hours of the killing of 15-year-old Alexandros Grigoropoulos. Hundreds of stores have been damaged or destroyed as gangs of masked youths and self-styled anarchists smashed windows with metal bars, looted stores and set up flaming street barricades in cities throughout Greece. Protests have spread beyond Greece's borders, with demonstrations in several European countries, including Italy, Spain and Denmark. Greek diplomatic missions have been vandalized in Istanbul and New York. Greece's conservative government has come under intense criticism for its handling of the crisis, despite authorities' insistence that they avoided heavy handed policing to prevent bloodshed. Prime Minister Costas Karamanlis, whose government has a single-seat majority in parliament, has ignored growing opposition calls for early elections. However, he has promised shopkeepers affected by riots handouts of â‚¬10,000 ($12,800) to cover short-term needs. An opinion poll published Wednesday showed 68 percent of Greeks disapproved of the government's handling of the crisis. Even before the riots, the Greek government was already facing public discontent over the state of the economy, the poor job prospects for students and a series of financial scandals. The protesters have begun adopting opposition demands for more financial relief for low-income Greeks. Greece's minimum wage is â‚¬658 ($850) per month. "We demand accountability, that this government resigns, and that this farce comes to an end," said 28-year-old Spyros Potamias, an architecture student who joined an occupation at Athens Polytechnic, where nightly riots have taken place. "This is about our future." Store owners have been shocked by the ferocity displayed by the rioters and by the extent of the destruction. "I can accept anger, I cannot accept looting," said Michael Lavdiotis, manager of a looted Athens coffee shop, where food and even furniture was stolen. "They took everything ... we're very frustrated. We didn't deserve this behavior." Greece's influential Orthodox Church has joined authorities in appealing for calm. "This tragedy cannot be resolved by burning and destroying the property of people who themselves have problems," said Church leader Archbishop Ieronymos. More student protests are planned for Friday.