By John Simpson, BBC World Affairs editor
Turkey has positioned itself with great care to be the go-between with Russia and Ukraine - and this seems to be paying off.
On Thursday afternoon, President Vladimir Putin rang the Turkish President, Recep Tayyip Erdogan, and told him what Russia's precise demands were for a peace deal with Ukraine.
Within half an hour of the ending of the phone call, I interviewed Mr Erdogan's leading adviser and spokesman, Ibrahim Kalin. Mr Kalin was part of the small group of officials who had listened in on the call.
The Russian demands fall into two categories.
