UNITED NATIONS, United States -- UN chief Antonio Guterres said Tuesday that it was time for Russia to end their "absurd war" in Ukraine, declaring the conflict "unwinnable."

The Secretary General told reporters at the world body's headquarters in New York that the war "is going nowhere, fast."

"For more than two weeks, Mariupol has been encircled by the Russian army and relentlessly bombed, shelled and attacked. For what?" he said.

"Even if Mariupol falls, Ukraine cannot be conquered city by city, street by street, house by house."

Guterres added that "the only outcome" to more fighting was "more suffering, more destruction, and more horror as far as the eye can see."

Negotiators from Moscow and Kyiv have held ongoing talks aimed at ending nearly four weeks of fierce fighting, but have failed to announce any progress so far.

Guterres said though that he believed diplomatic negotiations to bring a halt to fighting were making headway.

"There is enough on the table to cease hostilities now and seriously negotiate now.

"This war is unwinnable. Sooner or later, it will have to move from the battlefield to the peace table. That is inevitable," he added.

The UN General Assembly is due to reconvene a special emergency session on Ukraine on Wednesday and hold a vote this week on a non-binding French and Mexican resolution condemning Russia's invasion.

Earlier this month, 141 out of 193 United Nations member states supported a similar resolution.

The vote will indicate whether Russia has lost or gained any support over its actions since that vote on March 2.

South Africa, which abstained last time around, has circulated a rival draft resolution which calls for an end to hostilities but makes no mention of Russia as the aggressor.