Ukraine on Sunday warned of a possible escalation in fighting around the besieged southern port city of Mariupol after Moscow said it was focusing its military resources on capturing the eastern Donbas region. “This means a potential or sharp deterioration around Mariupol,” an adviser to the head of the President’s office, Oleksiy Arestovich, said in a video statement. He was referring to a surprise Russian statement on Friday that it was time for Moscow to set as its “main goal” controlling Donbas, an eastern region already partly held by Russian proxies. “This gives us hope in the area of Ky…