An elderly Greek man killed himself in Athens' busiest square today in protest at the country's debt crisis.

The incident sparked debate in parliament and an anti-austerity group called for a peaceful protest, accusing politicians of driving people to despair with harsh cutbacks implemented to secure vital international bailouts.

The 77-year-old drew a handgun and shot himself in the head near a subway exit on central Syntagma Square, which was crowded with commuters during the morning rush hour, police said. The square, opposite Greece's parliament, is a focal point for public protests.

Police said a hand-written note was found on the retired pharmacist's body in which he attributed his decision to the debt crisis.

Greece has seen an increase in suicides over the past two years of economic hardship, during which the country repeatedly teetered on the brink of bankruptcy.

Soon after the suicide, about a dozen written messages had been pinned to the tree under which the man shot himself, some reading "It was a murder, not a suicide," and "Austerity kills."

A government spokesman described the incident as "a human tragedy," but said it should not become part of political debate.

"I don't know the exact circumstances that led that man to his act," he said. "I believe we must all remain calm and show respect for the true events, which we do not yet fully know."

Anti-austerity activists who had held daily protests for months last year at Syntagma Square blamed the suicide on the cutbacks and called for a new protest in the evening.

Greece has relied on international rescue loans since May 2010. To secure them, Athens implemented harsh austerity measures, slashing pensions and salaries while repeatedly raising taxes.

But the belt-tightening worsened the recession, and led to thousands of job losses with one in five Greeks currently unemployed.