Fresh clashes have broken out between police and protesters in at least three Greek cities, after the fatal shooting of a 15-year-old boy by police.
Picture taken by Filoktitis Salaminios on Sunday in Athens
About 300 students battled police in Thessaloniki, while protests turned violent in Trikala and Piraeus.
BBC website readers have been giving their reaction to the worst violence Greece has witnessed in several years .
On the bus from Piraeus. Small explosion in street outside bus at 12:03GMT. Rattled the bus windows. Hundreds of young people in the street scattered. Some were wearing hoods and masks. Sounded equivalent to a small stick of dynamite. (No worse than you hear at the Greek Easter!) Several water cannons seen. Some streets closed off. Bus loads of police. Several fire engines present. 1-2 km from Piraeus Port near the Dimotiko Theatro bus stop.
Malcolm Brown, from Marazion, UK
In the town of Karlovasi, Samos Island there was only a peaceful street demonstration mainly by school kids.
Efpalinos, Samos, Greece
I was visiting the town centre this morning and was only yards away from the mass of students (200 or so) in Alexandras street. There was lots of shouting and cheering for about five minutes, but then the rocks started flying. It was an amazing/shocking sight. Some kids then started to climb over the high railings of the police station at which point shots were fired and tear gas tossed into the main body of the crowd. Most of the students dispersed at that point as the whole area was engulfed in gas.
Peter Hughes, Kerkyra (Corfu town), Greece
There is no doubt that the situation is being exploited by groups for their own political agenda, nor that police brutality exists. Many of the police work for 600 Euros a month and are the same age as the protesting students. They are ill trained to carry firearms. In Exarchia today it is quiet and subdued, there is a respectful peace around the place where Alexandros was killed. Small businesses are clearing up the debris, coffee shops are open, the bookshops are mending their windows, and one old person turned to me and asked as I lay a rose - 'Ti na kanoume?" What can we do? Many feel helpless in the stand off between left and right.
Jerry Goldstein took this picture in Exarchia on Monday.
Lauren O'Hara, Athens - Exharchia
It's now clear that the death of the 15-year-old boy was the spark that lighted the fire throughout Greece. The government and the mass media can no longer refer to the people clashing as anarchists or "troublemakers" as today it was students the same age as Alex that took to the streets spontaneously. It was their time to respond to a brutality that has been long present in this part of Europe. As the slogan says "This bullet wasn't for Alex, it was for us"
Logan, Athens, Greece
Our society is in tatters. Five years of conservative government in Greece and what is left? The country is bankrupt and burned down, people are struggling to make ends meet. Justice has been raped in this country for decades. We deserve the leaders we choose, but we the generation Y of Greece are here to say that enough is enough. We have brains, we think and have feelings, yes we want change.
Dimitri Panagiotou, Serres, Greece