DEREK GATOPOULOSATHENS, Greece (AP) â¿¿ Hundreds of youths pelted riot police with fire bombs, bottles and chunks of marble Thursday as yet another Greek anti-austerity demonstration descended into violence, less than a month after more intense clashes broke out during a similar protest. Authorities said around 70,000 protesters took to the street in two separate demonstrations in Athens during the country's second general strike in a month as workers across the country walked off the job to protest new austerity measures the government is negotiating with Greece's international creditors. Thursday's strike was timed to coincide with a European Union summit in Brussels later in the day, at which Greece's economic fate will likely feature large. Riot police responded with volleys of tear gas and stun grenades in the capital's Syntagma Square outside Parliament as protesters scattered during the clashes, which continued on and off for about an hour. Another general strike in late September had also seen limited, but much more intense, clashes between protesters and police. A 65-year-old protester suffered a fatal heart attack during the demonstration but efforts to revive him failed. The organizers of the protest march he participated in said the man had fallen ill before any rioting had broken out. Four demonstrators were injured after being hit by police, volunteer paramedics said. The Health Ministry said two of the protesters were treated in hospital and that their injuries were not serious. Three policemen also required hospital treatment. Hundreds of police had been deployed in the Greek capital ahead of the demonstration. Police said seven people were arrested Thursday, out of more than 100 detained. The strike grounded flights, shut down public services, closed schools, hospitals and shops and hampered public transport in the capital. Taxi drivers joined in for nine hours, while a three-hour work stoppage by air traffic controllers led to flight cancellations. Islands were left cut off as ferries stayed in ports.