Hundreds of youths have pelted riot police with petrol bombs, bottles and chunks of marble as yet another Greek anti-austerity demonstration descended into violence.
A 65-year-old protester suffered a fatal heart attack during the demonstration, the Health Ministry said. The man was taken to hospital but efforts to revive him failed.
It was not immediately clear whether the protester had been caught up in the rioting when he fell ill.
Authorities said around 70,000 protesters took to the street during the country's second general strike in a month as workers across the country walked off the job to protest at new austerity measures the government is negotiating with Greece's international creditors.
The measures for 2013-14, worth 13.5 billion euro (£11 billion), aim to prevent the country from going bankrupt and potentially having to leave the 17-nation eurozone.
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.
Four demonstrators were injured after being hit by police, paramedics said. The Health Ministry said two of the protesters were treated in hospital and that their injuries were not serious. Hundreds of police had been deployed in the Greek capital ahead of the demonstration. Police said about 50 people were detained.
A similar demonstration by about 17,000 people in the northern city of Thessaloniki ended peacefully.
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.