Ukrainian President Volodymyr Zelenskiy has asked the head of the United Nations to help save the lives of the remaining Ukrainians trapped in the Azovstal steel plant in Mariupol.

“The lives of the people who remain there are in danger. Everyone is important to us. We ask for your help in saving them,” Zelenskiy told UN Secretary-General Antonio Guterres in a phone call on May 4.

He called on the UN to “assist in the removal of all the wounded from Azovstal,” a statement from his office said.

The statement came as Ukraine said that there were fierce battles with Russian troops at the plant, where Ukrainian soldiers had been holed up for weeks.

Zelenskiy also thanked Guterres for evacuations earlier this week led by the UN and the Red Cross (ICRC), which he said brought more than 100 people out of the Azovstal complex to safety.

“The whole world has learned about the role of the UN and the ICRC. This has shown that international organizations can be effective,” he said.

He “expressed hope for a successful continuation of the ongoing evacuation operation.”