Ukrainian Marines trying to defend the city of Mariupol from the onslaught of the Russian army says they've been fighting for more than a month without resupply of ammunition, food and water – but now the "mountain of wounded makes up almost half of the crew."

The dire warning from the 36th Navy Brigade, which was posted to Facebook on Sunday, suggests cracks are starting to form in Ukraine’s fierce defense of Mariupol.

"From the beginning... we have been defending Mariupol for 47 days," the Marines wrote. "We were bombed from airplanes, we were shot from artillery, tanks and other fire materials. We kept the defense worthy by doing the impossible. But any resources have a potential to run out."

A resident looks on near a building destroyed in the course of the Ukraine-Russia conflict in the southern port city of Mariupol on Sunday. (REUTERS/Alexander Ermochenko)

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"For more than a month, the Marines fought without refilling ammunition, without food, without water... [but now] the mountain of wounded makes up almost half of the crew," it continued. "Those who have unbroken limbs and can walk, return in order."

The Marines also say their unit is "dying but fighting" and "gradually we are coming to an end."

Graves of civilians killed during Ukraine-Russia conflict are seen next to apartment buildings in Mariupol on Sunday. (Reuters/Alexander Ermochenko)

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"Further is death for some, but captivity for some," it said. "I don't know what's next, but I really ask you to remember the Marines with a kind word and no matter how they develop further, do not talk badly about the Marines."

A view inside the theater damaged during fighting in Mariupol in eastern Ukraine, on April 4, 2022. (AP/Alexei Alexandrov)

"They did everything possible and impossible," the statement concluded.

Ukraine Marine unit in Mariupol: 'Gradually we are coming to an end'

Ukraine has been trying to prevent Russia’s army from capturing Mariupol