Germany's finance minister is cautioning Greek politicians against promising things they can't deliver in upcoming elections and making clear that he opposes a new debt write-down for Athens.

Greece will hold elections on Jan 25, with polls pointing to a first-place finish for the anti-bailout Syriza party. Syriza is demanding that more than half of the Greek bailout debt be canceled.

Asked about that demand, German Finance Minister Wolfgang Schaeuble said told the weekly Der Spiegel published on Saturday that "this question doesn't arise". He said the next government must keep to existing agreements because "that is in the interest of the Greeks".

Schaeuble said: "Politicians in Greece must take care that they don't promise more before the election than they can keep afterward."

AP