Greek police have fired tear gas to control a demonstration of pensioners protesting over cutbacks to their benefits, part of an austerity drive dictated by international lenders.
About 1500 pensioners attempted to march to Prime Minister Alexis Tsipras's office on Monday but riot police blocked their path.
Tensions flared when dozens of pensioners attempted to push over a police bus blocking their way a few hundred metres from Tsipras' office.
The left-led government is expected to submit its budget for 2017 in parliament on Monday evening (local time).
Greece has been reeling from the impact of incessant rounds of austerity for the past seven years, dictated by creditors as a remedy for years of financial mismanagement which culminated in three international bailouts.
Pensioners have been particularly hit, with many benefits pared as taxes have spiked.
"Is it possible that I should pay the same real estate tax as a rich businessman?" asked Nikos Saslov, a civil servant due for retirement next year.
"If they (the government) are leftists, then I'm Sophia Loren," the greying bespectacled man in sandals said, referring to the Italian actress.