Russian troops are "amassing their forces" to concentrate military attacks in eastern Ukraine because they failed in other areas, President Volodymyr Zelensky's spokesman has said.
Sergey Nikiforov told the BBC's Sunday Morning show that Vladimir Putin's soldiers are "regrouping" and preparing to "encircle our military in Donbas".
He said: "They're pulling back in some regions… They're pulling back to Belarus, to Russia, they're regrouping and then they're aimed to strike at Donbas. They're amassing their forces. They're preparing to concentrate their efforts in the east.
"The only part of Ukraine where they are having some progress is the east."
Residents of Ukraine's besieged south-eastern coast were awaiting possible evacuation on Sunday as the country's president said Russia's obsession with capturing a key port city has left it weakened and created opportunities for his troops.
It came as Russia said its military had struck an oil processing plant and fuel depots around the strategic Black Sea port of Odesa.
Russian Defence Ministry spokesman Major General Igor Konashenkov said Russian ships and aircraft fired missiles to strike the facilities, which he said were used to provide fuel to Ukrainian troops near Mykolaiv.
Watch: Ukrainian defenders display improvised attack drones.
Maj Gen Konashenkov said Russian strikes also destroyed ammunition depots in Kostiantynivka and Khresyshche.
With Mariupol, to the east of Odesa, squarely in Russia's crosshairs, Ukraine insists it has gained a leg up elsewhere in the country, leading to troops retaking territory north of the capital, Kyiv, as Russian forces departed.
"Ukraine has gained invaluable time, time that is allowing us to foil the enemy's tactics and weaken its capabilities," President Volodymyr Zelensky said late on Saturday.
However, inside Mariupol, which has been surrounded by Russian forces for more than a month and suffered by some of the war's worst attacks, conditions remain dire and prospects for escape uncertain.
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