Some 32,000 people took to the streets of Greece on Monday to mark the 41st anniversary of a deadly student uprising that sparked the country's return to democracy in the 1970s.
As the march that officials said drew 18,000 people in Athens was winding down, the 7,000-strong police contingent used tear gas and stun grenades to disperse a crowd burning American and European Union flags in front of the US embassy.
Some 14,000 demonstrators in Greece's second largest city Thessaloniki, who were watched over by 1,000 police, went home peacefully.
The march, which is a left and labour union tradition in Greece, commemorates the November 17, 1973, Athens Polytechnic university student uprising against the then ruling military dictatorship.
More than 20 people were killed in clashes that day, but it marked the beginning of the end for the junta that had held power since 1967, with democracy being restored seven months later.
Each year the demonstrators march to the US embassy for a protest to denounce the role US intelligence agents played in the military dictatorship's rise to power.
In recent years demonstrators have also used the anniversary to voice opposition to the harsh austerity measures imposed on Greece by its international creditors after the global financial crisis.
"At a moment when the government is trying to remove all sense of social justice through austerity measures, the demands of the Polytechnic remain current," the General Confederation of Greek Workers (GSEE), the country's main union, said in a statement.
Last week students clashed with security forces in front of Athens Polytechnic over a decision by the head of the University of Athens to shorten by one day the annual three-day shutdown of the school for the uprising anniversary.