The Ukrainian government, the British government and others predict that ‘Mariupol’ will be the next city that the Donetsk People’s Republic will attempt to seize from Ukrainian control....the city isn’t as important to the separatists as it is to Ukraine for they would lose its largest port on the Azov Sea.... but it certainly is significant for Russia.... a land bridge with Crimea.
In addition, Mariupol is an important industrial city. It would devastate Ukraine to lose it.