What is Russia's vision of a federal Ukraine?
Russia is pushing for Ukraine to become a federation - prompting a sharp response from Kiev that it should put its own house in order first. But what does Moscow have in mind?
In Russia's view, a federal Ukraine would see its regions given much more power over the local economy, finance and foreign trade, as well as language, traditions, religious practices, education, cultural ties abroad and relations with neighbouring states, including Russia.
These regions, according to Russian Foreign Minister Sergei Lavrov, would be responsible for making sure the rights of minorities were respected.
In addition, regional legislative assemblies and governors would be voted in through local elections so that Kiev could not impose its choice of governor on a region (as it does now).
Kiev would retain state-wide functions like defence, foreign policy and the legal system - in other words, central government would be much diminished.
How would this reform come about?
Russia Foreign Minister Sergei Lavrov has repeatedly said that neither Russia - nor any other outside power - should try to impose a framework, but leave it up to Ukrainians themselves to decide on how it would work.
The question is which Ukrainians? The US argues that the Kiev government must be in the lead.
But Moscow argues that Kiev - a temporary government which it claims came to power in an illegal coup - should not have a veto over what happens, but instead invite all political forces and regions to join a nationwide dialogue, where all participants would have an equal voice and vote.
That would mean the central government could not impose its own plan on others. But it could also give the regions the upper hand when it comes to deciding which powers to strip away from the centre.
Russia also proposes that, once agreed, the new framework should be put to a nationwide referendum, which must take place ahead of any national election (in theory ahead of the presidential election planned for late May).
Last week, Ukraine's ousted President Viktor Yanukovych, now in exile in Russia, said the nationwide referendum could determine the status of each of Ukraine's regions, suggesting different regions might be allowed to seek more or less autonomy from the centre as they saw fit.
What if some regions opted for secession?
Already some pro-Moscow groups in largely Russian-speaking cities like Donetsk and Kharkiv have aired the possibility.
And Russian President Vladimir Putin has hinted that they too would be welcome to join Russia. He has described Ukraine's southern and south-eastern regions as historically Russia's lands, and implied their allocation to Ukraine by the Bolsheviks after the 1917 Revolution was a mistake.
Why is Moscow so insistent on this reform?
Russia's argument is that Ukraine cannot survive as a unitary state and only by turning it into a looser federation could different regions keep their separate identities and sometimes conflicting interests without coming to blows.
So that federalising Ukraine, far from making it weaker and more likely to fracture, could actually help keep it together.
More specifically, the Russian government warns that this is the only way to protect the rights of minorities like Russian-speakers from the radical Ukrainian nationalists they claim are dictating policy in Kiev.
But those suspicious of Russia's motives fear that the real intention is to weaken the central Kiev authorities.
This could turn into a mechanism to allow regions to secede and join Russia or decision-making would be constantly subject to approval from regional governments, some of which Russia might hope would be closely allied to Moscow, thereby allowing it to influence Ukraine's allegiances and policies.
Which regions might want to loosen ties with Kiev?
Russia has focused its attention on eastern and southern regions where Russian speakers predominate and where a majority voted for Viktor Yanukovych in Ukraine's last presidential election. These include the cities of Kharkiv, Luhansk , Donetsk and Odessa, where there have been pro-Russian demonstrations and even attempts by some pro-Moscow groups to take over local governments and assemblies.
But the result of any vote or referendum is hard to predict. It would depend on the circumstances and on what questions were offered.
It is by no means certain that in each of these regions a majority would opt for closer ties to Russia if it meant weakening Ukrainian statehood.
And if - as in Crimea - troops were deployed or there were other reasons for voters to feel intimidated or swayed by a powerful onslaught of propaganda, it might affect how people voted or where there was a boycott.
What response has there been from the West?
US Secretary of State John Kerry has indicated that the US is not against the idea of a federation as a possible way to find a diplomatic exit from the crisis, but only if Ukraine itself agrees to it.
And he has been very firm that it would be up to the interim government in Kiev to approve it.
What has been the response in Kiev?
Kiev is apparently prepared to consider giving more local powers to regions, but so far it has been firmly against the idea of a federation.
The Ukrainian foreign ministry dismissed it as a plan with only one aim: to split and destroy Ukrainian statehood.
Moreover, the acting Ukrainian foreign minister has said he is worried there are plans afoot to destabilise Ukraine's eastern and southern regions in order to give Russia a pretext to create a corridor through Ukraine which would link up Russia, Crimea, and the largely Russian-speaking enclave of Trans-Dniester - a breakaway part of Moldova on Ukraine's western border.
In recent days Russia has warned that it is extremely concerned about what it says is a blockade of Trans-Dniester by Ukraine's new government, calling it intolerable and outrageous. Concerns have been raised in Nato that Russia might have plans to intervene there militarily.
How would a Ukrainian federation compare with Russia?
Russia is also a federation, made up of over 80 subjects, including national republics that are home to specific ethnic minorities, as well as autonomous districts and regions.
The degree of autonomy and self-government of each unit depends to some extent on its status, but it has also depended on who is in power in the Kremlin.
In the 1990s under President Boris Yeltsin there was more self-government in the regions.
Some republics like Tatarstan (a republic in Central Russia dominated by distant cousins to the Crimean Tatars) had considerable self-rule, granted in part to placate them and stop them seeking to break away from Russia like the separatist movement in Chechnya.
But when President Putin came to power in 2000, one of his first reforms was to impose more control over regions, precisely in order to strengthen central government and weaken challenges from the periphery.
Most importantly, he ordered that the bulk of taxes should be transferred to the centre, making most regions dependent on Moscow's patronage.
In 2004, he also abolished direct local elections for governors, giving himself as president the right to appoint them. In 2012 President Medvedev reinstated direct elections for governors. But candidates are still subject to presidential approval, giving the Kremlin considerable leverage over regional leaders.
The irony of President Putin having a reputation for enforcing central rule in Russia, while advocating the opposite in Ukraine, has not been lost on Kiev politicians.
The Ukrainian foreign ministry suggested Russia should perhaps start with reforming its own federal arrangements, before telling Ukraine what to do.