Greek protesters clash with police

Greek protesters have hurled firebombs and stones at police outside parliament, while unions grounded flights and shut down public offices in a 13th day of anti-government protests since police shot dead a teenager.

Demonstrators waving red flags jostled with police, who had formed a cordon around parliament, and attempted to burn down a  Christmas tree in the square outside.

Police fired teargas to disperse the crowd who carried banners with slogans such as "Down with the government of blood, poverty and privatisations".

About 7,000 people took part in the protest against the government's social and economic reforms, which many Greeks say have failed to shelter Greeks from the global economic crisis, and which were unleashed by the teenager's killing.

Dual factors

Speaking to Al Jazeera, Leonidas Gotzes, head of international relations at the New York College in Athens, said there were both internal and external factors in explaining the continuing violence.

Gotzes said: "There seems to be a lot more [happening] than meets the eye. There are those that believe that there are forces working both from within and from without.

"Specifically, from within there are opposition groups, anarchists, the radical left, that seem to have jumped on the bandwagon here and are trying to destabilize the government.