BBC: 'The Russian demands fall into two categories.
'The first four demands are, according to Mr Kalin, not too difficult for Ukraine to meet.
Chief among them is an acceptance by Ukraine that it should be neutral and should not apply to join Nato. Ukraine's President Volodymyr Zelensky has already conceded this.
'There are other demands in this category which mostly seem to be face-saving elements for the Russian side.
'Ukraine would have to undergo a disarmament process to ensure it wasn't a threat to Russia. There would have to be protection for the Russian language in Ukraine. And there is something called
''The second category is where the difficulty will lie, and in his phone call, Mr Putin said that it would need face-to-face negotiations between him and President Zelensky before agreement could be reached on these points. Mr Zelensky has already said he's prepared to meet the Russian president and negotiate with him one-to-one.
'Mr Kalin was much less specific about these issues, saying simply that they involved the status of Donbas, in eastern Ukraine, parts of which have already broken away from Ukraine and stressed their Russianness, and the status of Crimea.
'Although Mr Kalin didn't go into detail, the assumption is that Russia will demand that the Ukrainian government should give up territory in eastern Ukraine. That will be deeply contentious.
'The other assumption is that Russia will demand that Ukraine should formally accept that Crimea, which Russia illegally annexed in 2014, does indeed now belong to Russia. If this is the case, it will be a bitter pill for Ukraine to swallow.'