Chancellor Angela Merkel on Tuesday said Germany could "not stay silent" on EU fears about the rule of law in neighbouring Poland, calling it a "serious issue".

Poland on Monday rejected EU concerns that the rightwing government's controversial court reforms, which have sparked street protests, will erode judicial independence in the former communist state.

Merkel said: "as much as I want good relations with Poland, our neighbour ... we cannot stay silent and say nothing just to keep the peace" while stressing that the rule of law was "the basis for cooperation within the EU".