Greek unrest after pensioner suicide beside parliament
The 77-year-old man killed himself in the city's busy Syntagma Square on Wednesday morning.
Greek media reported he had left a suicide note accusing the government of cutting his pension to nothing, BBC News reports.
Flowers have been laid at the spot where he died and tributes have been paid online.
Hundreds of demonstrators gathered in the square outside parliament on Wednesday evening, the scene of many large protests in recent months.
Violence erupted, with petrol bombs hurled at police, who fired tear gas in response.
Depression and suicides are reported to have increased in Greece as the country introduces tough austerity measures to deal with huge debts.
'Dignified end'
The man has not been officially identified but was named in Greek media as Dimitris Christoulas. He was said to be a retired chemist, with a wife and a daughter, who had sold his pharmacy in 1994.
He shot himself in the central square just before 09:00 (06:00 GMT), Athens News reports.
The unemployment rate is now over 20% and a similar number is below the poverty line.
The suicide rate in Greece used to be the lowest in Europe but it has soared during the crisis.
Behind the figures there is a society that is feeling intense pain.
As you walk around the streets of Athens and beyond you can see the signs of a broken society.
Homelessness is on the rise, shops are closing and there has been a rise in anti-immigrant violence.
There is another Greece as well - the Greece that continues to persevere, where people go out and enjoy themselves.
But it is also a nation that is deeply troubled and that is likely to be expressed in early elections that are expected in about five or six weeks.
In the alleged suicide note, found by police and reported by Athens News, he said: "The government has annihilated all traces for my survival, which was based on a very dignified pension that I alone paid for 35 years with no help from the state.
"And since my advanced age does not allow me a way of dynamically reacting... I see no other solution than this dignified end to my life, so I don't find myself fishing through garbage cans for my sustenance."
Dozens of people left handwritten messages and flowers at the spot where Mr Christoulas killed himself.
One of the notes, pinned to the tree, read "Enough is enough", while another said "Who will be the next victim?"
Later, as night fell, the demonstrations degenerated into clashes as activists threw rocks and petrol bombs at police, who responded with tear gas and flash grenades.
Prime Minister Lucas Papademos issued a statement calling the death "tragic".
"In these difficult hours for our society we must all - the state and the citizens - support the people among us who are desperate."
Government spokesman Pantelis Kapsis called the suicide a "human tragedy" but said "the exact circumstances" were unknown.
Details also at http://www.bbc.co.uk/news/world-europe-17620421