Ukrainian President Volodymyr Zelensky called Tuesday on Pope Francis to mediate in his country's conflict with Russia to help alleviate human suffering, nearly one month into Moscow's invasion.

Zelensky said he had held a telephone call with the pope and that he had "told His Holiness about the difficult humanitarian situation and the blocking of rescue corridors by Russian troops."

"The mediating role of the Holy See in ending human suffering would be appreciated," Zelensky wrote on Twitter following the call.

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.

Pope Francis, who is due to visit Malta next month. has called for an end to the conflict on more than one occasion, and although he has condemned the "massacre" in Ukraine, he has avoided mentioning Russia by name.

Russian Orthodox Patriarch Kirill and Francis earlier this month held talks on Ukraine and urged negotiations to continue to reach a "just peace".

Shortly after the start of Russia's military operation last month in Ukraine, Patriarch Kirill called Moscow's opponents in Ukraine "evil forces".