Russian forces are attempting to establish full control over the besieged city of Mariupol, Ukraine’s armed forces said, ahead of what is expected to be an intense wave of fighting in the country’s east as Moscow strengthens its positions there.

The fate of Mariupol, a port city on the Sea of Azov that has been the site of some of the war’s most intense shelling, carries strategic and psychological importance. If Russia takes control of the city, it would be a significant mark of progress as it expands out from areas it already controls in the Donbas region toward the Crimean Peninsula, which it annexed in 2014.