"The conditions for that will be negotiated between the two parties, as it can only be, because they know the details of a negotiation that nobody else would be aware of," Trump s

The Vatican has a long history of conflict mediation, with varying degrees of success. An effort by the pope to end the war in Ukraine would face long odds.

The crucial fight being slugged out between Russia, Ukraine and their allies is for the ear of US President Donald Trump, who seems increasingly frustrated with efforts to broker peace.