The fresh round of painful austerity measures Greek coalition party leaders agreed to on Thursday in exchange for further aid by international lenders to avert a default in March sparked strong reactions in Athens.

A few hours after an official statement by Prime Minister Lucas Papademos that the leaders of parties supporting his transitional administration clinched a full agreement on the policies negotiated with the European Union (EU)/International Monetary Fund (IMF) creditors, socialist Deputy Minister of Labor Yannis Koutsoukos tendered his resignation.

"Our creditors ignored our arguments in an unacceptable manner that amounts to blackmail, imposing measures that destroy labor relations," he said in a letter addressed to Papademos and released to Greek media.

His resignation fuelled scenarios of a cabinet reshuffle in the coming days and the prospect of snap general elections sooner than April as expected, amid rumors that the small rightist Popular Orthodox Rally (LAOS) party could announce a walkout from the coalition on Friday.

The new set of harsh cuts on salaries and pensions of private sector employees and plans for some 15,000 layoffs of civil servants this year to secure the second 130-billion-euro (172.89 billion U.S. dollars) bailout package and a voluntary write-down of part of the Greek debt owned by private creditors have triggered anger in Greece.

Beyond sighs of relief by a part of Greek society that believes the measures will contribute to efforts to slash deficits and boost development to exit the crisis, critics argue that they will deepen recession.

Further austerity will downgrade to "junk status" the living standards of average Greek households, as the local daily NEA commented characteristically.

As Finance Minister Evangelos Venizelos was set to present the details of the deal at a Eurogroup meeting in Brussels on Thursday evening, thousands of protesters hit the streets of central Athens in two rallies organized by leftist opposition parties, calling on people to "resist" and demand early elections.

Public Electricity Company employees, health personnel and policemen held a string of smaller marches and symbolic sit-ins at ministries against the austerity drive. Representing the business community, President at the Athens Chamber of Commerce and Trade Konstantinos Michalos talked of "shock-and-awe measures."

The two main unions of private and public sector workers GSEE and ADEDY called for a new 48-hour general strike on Friday and Saturday and further demonstrations in front of the assembly building, where deputies will be debating the agreement.

Ahead of a parliamentary vote scheduled for Sunday night, a growing number of MPs of the coalition parties warned on Thursday that they would reject further austerity.

But, without further aid by international creditors in time so that Athens can pay off a 14.5-billion-euro (19.28 billion dollars) bond payment due on March 20, Greece could collapse, causing market turmoil across Europe and even the world.

The debt-laden country has managed to stay afloat since 2010 due to international rescue loans and has pledged a painful austerity and reform drive that has missed targets.