German Catholic bishops on Monday called on the Vatican to clarify remarks in which Pope Francis said Ukraine should have "the courage of the white flag" and negotiate an end to the conflict with Russia.

Francis' comments, made in an interview with Swiss broadcaster RSI that has yet to be aired but whose contents were revealed at the weekend, have been rebuffed by Ukraine and welcomed by Russia.

In a statement published on its website, the German Bishops' Conference said it was ultimately up to Ukraine to decide, "after careful consideration, when the moment has come for peace negotiations."

"The fact that Pope Francis did not address the points mentioned here in his interview caused irritation among many observers, which we can understand. It would be good if the Holy See communicated a substantive clarification of its position on these issues," German bishops said.

In the interview Francis was asked for his position on a debate between those who say Ukraine should give up, as it has not been able to repel Russian forces, and those who say doing so would legitimise actions by the strongest party. The interviewer used the term "white flag" in the question.

Vatican spokesman Matteo Bruni said on Saturday the pope had picked up on the term "white flag" and used it "to indicate a stop to hostilities (and) a truce achieved with the courage of negotiations".

German bishops said it was "unfortunate" that Francis repeated the words "white flag", but also said it was "self-evident and widely proven to us that the Pope – like the German Bishops' Conference – is committed to a just and lasting peace in Ukraine."