UN Secretary-General Antonio Guterres said Wednesday that a "ceasefire in Ukraine doesn't seem possible," indicating that the United Nations was still waiting for answers from Russia to proposals for evacuating civilians and delivering aid.

"That was our appeal for humanitarian reasons, but it doesn't seem possible," he said at a press conference.

Guterres recently sent UN humanitarian chief Martin Griffiths to Moscow and Kyiv with the goal of cementing a ceasefire.   

Aid agencies have repeatedly tried to evacuate civilians from Ukrainian cities such as Mariupol, besieged for weeks by Russian invading forces.

Asked if he believed a "genocide" was underway in Ukraine, as US President Joe Biden said on Tuesday, the UN chief was careful not to use the term.

"Genocide is strictly defined in international law. And for the UN, we rely on the final legal determination by the appropriate judicial bodies," he said, noting that an investigation into the war in Ukraine had been opened by the International Criminal Court based in The Hague. 

Guterres also urged the International Monetary Fund and the World Bank, which are due to hold their spring meetings in Washington soon, to release money for developing countries suffering from the invasion's fallout.

The UN says 69 countries -- nearly a third of them in Africa -- are feeling the impact on food supplies, energy resources and financial systems.

"The money is there, it needs to be used," Guterres said.