Greek Communist party labour union supporters occupied the finance ministry on Thursday (11 June) and prevented staff from entering over fears that the government will agree to further concessions in order to come to a cash-for-reform deal with lenders.
As ratings agency Standard & Poor's downgraded Greek bonds further into junk status, questioning whether Athens can pay its debts, Greek prime minister Alexis Tsipras held a new round of late-night talks on Wednesday (10 June) with the leaders of Germany and France and expressed confidence that a solution was at hand.
"The prime minister's statement about the (upcoming) deal and how it is going well, is like a declaration of war on the working classes," said protester Effie Malliou.
Talks with lenders have been deadlocked over Greece's rejection of the creditors' demands for cuts in pensions and unpopular labour market reforms as conditions for releasing frozen bailout funds.
"There is no way we can endure any more under austerity, the working class's income has already suffered a lot," added Malliou.
Greece will be in default at the end of June without fresh funds to let it to repay €1.6bn (£1.17bn, $1.81bn) to the IMF. It put off a smaller repayment earlier this month under a rarely used IMF rule allowing it to combine all payments due in any month.
While both sides may be holding out to see if the other blinks first, time is running out and Tsipras faces pressure not just from left-wing hardliners but also from Greek voters, most of whom say they want to remain in the euro zone.
A poll showed a slight rise since April in the number of people dissatisfied with Tsipras's negotiating performance with the creditors, reaching 53.4 percent from 50.5 percent.