Greece's new left-wing government is insisting it will stick to its anti-austerity agenda, hours after the European Central Bank tightened the screws on Athens by withdrawing a key borrowing option for the country's banks.

Government spokesman Gavriil Sakellaridis says Greece is not using blackmail in its bid to win over bailout creditors, but "will not be blackmailed" either.

Late Wednesday, the ECB said it would stop allowing Greek banks to borrow from it cheaply using Greece's junk-rated government bonds as collateral, as prospects for a new deal with bailout creditors appear uncertain.

The move, ahead of Thursday's key talks in Berlin between the Greek and German finance ministers, increases pressure on Athens to compromise with its creditors. Greek banks retain access to emergency lending, but at a higher cost.