"We, all of the military personnel in the garnison of Mariupol, we have witnessed the war crimes performed by Russia, by the Russian army. We are witnesses. Surrender is not an option because Russia is not interested in our lives," said Ilya Samoilenko, an Azov regiment intelligence officer.

The Azovstal steel mill is the last pocket of Ukrainian resistance in the devastated port city and its fate has taken on a symbolic value in the broader battle since Russia's invasion.

"All our supplies are limited. We still have water. We still have munitions. We will have our personal weapons. We will fight until the best resolution of the situation," Samoilenko said.

Ukraine has said that all women, children and elderly civilians have been allowed to flee from Azovstal as part of a humanitarian mission coordinated by the United Nations and the Red Cross.