Protesters hung two giant banners off the Acropolis on Wednesday, with slogans calling for mass demonstrations and 'resistance' after days of violent protest sparked by the fatal police shooting of a teenager in Athens. About a dozen protesters held the pink banners over the walls of the ancient citadel, Greece's most famous monument, one bearing the word "Resistance" written in large black letters in four languages: Greek, English, Italian and German. The other called for mass demonstrations across Greece on Thursday. The riots that followed the Dec. 6 police killing of 15-year-old Alexandros Grigoropoulos are the worst Greece has seen in decades, feeding off widespread dissatisfaction with the unpopular conservative government and anger over social inequality and economic hardship. Hundreds of shops and banks were smashed, torched or looted as gangs of masked and hooded youths rampaged through cities night after night, setting up burning barricades in the streets and clashing with riot police who fired large amounts of tear gas. Retailers say the damage will cost them euro1.5 billion ($2 billion) in lost income. More than 300 people were detained or arrested in the rioting. Protesters are planning a rally outside the main court complex in Athens later Wednesday to demand the release of all those arrested. After a week of widespread violence, many protesters have begun using different tactics to make themselves heard. On Tuesday, a group of youths forced their way into Greece's state television and radio studios, forcing broadcasters to put out anti-government messages. Ten young protesters disrupted a state NET television news broadcast of the prime minister's speech, appearing live on national television for just over a minute, carrying banners that read: "Stop watching, get out onto the streets" and "Free everyone who has been arrested." In Greece's second largest city of Thessaloniki, protesters broke into three local radio stations, agreeing to leave only when a protest message was read out on the air. Protesters taking over the airwaves was the latest embarrassment for Prime Minister Costas Karamanlis' conservative government, which is still grappling to quell days of rioting in Greek cities. Greece's opposition Socialists, who are calling for early elections, have accused Karamanlis of mishandling the crisis, which they said had worsened the effects of the global economic downturn. "Greeks are losing their patience. Their salary is running out before the end of the month as they endure a major economic crisis, and at the same time can see the state collapsing," Socialist spokesman Giorgos Papaconstantinou said Tuesday. Despite the change in tactics, some violence has persisted. In Thessaloniki, police said a bank and a local citizens advice office were firebombed before dawn Wednesday in attacks that caused damage but no injuries. Such attacks, usually attributed to the work of far-left radical groups, occur frequently in Athens and Thessaloniki and rarely cause any injuries. On Tuesday, Thessaloniki riot police fired tear gas to disperse 300 youths throwing fruit and stones outside the city's main court complex. The disturbance followed a court decision that found eight police officers guilty of abusing a student following riots two years ago. In the capital, about 30 youths threw petrol bombs and stones at the riot police headquarters, damaging seven cars and a police bus parked outside. No injuries were reported.