A humanitarian ceasefire in Ukraine does not seem possible at the moment, United Nations Secretary-General Antonio Guterres said on Wednesday.

Since the beginning of April U.N. aid chief Martin Griffiths has visited Russia and Ukraine to see if a humanitarian truce could be agreed.

"At the present moment a global ceasefire in Ukraine doesn't seem possible," Guterres told reporters.

Since Russia invaded Ukraine on Feb. 24, thousands have been killed and the United Nations said some 11 million Ukrainians - more than a quarter of the population - have fled their homes. More than 4 million of those people have left Ukraine.

"There are lots of things that can be done in order to guarantee evacuation of civilians," said Guterres.

He said the United Nations had made proposals to Russia to "bring the parties together and to manage" humanitarian access, local ceasefires and the evacuation of civilians. He said the United Nations was waiting on a response from Russia.