As he briefed the UN Security Council on his shuttle diplomacy last week in Russia and Ukraine, Guterres said that he "did not mince words" when he spoke with the presidents of Russia and Ukraine about ending the conflict, Xinhua news agency reported.
The conflict must "end for the sake of the people of Ukraine, Russia, and the entire world...the cycle of death, destruction, dislocation and disruption must stop," the secretary-general said at a Security Council meeting on the situation in Ukraine.
"In my meeting with (Russian) President Putin, I therefore stressed the imperative of enabling humanitarian access and evacuations from besieged areas, including first and foremost, Mariupol," said Guterres, appealing strongly for a safe and effective humanitarian corridor for civilians to reach safety from the Azovstal plant, where hundreds have been living underground for weeks.
"We must continue to do all we can to get people out of these hellscapes," said the UN chief.
Reporting on "some measure of success," Guterres outlined the complex humanitarian operation underway, led by the UN and the International Committee of the Red Cross.
"It began on April 29 and has required enormous coordination and advocacy with the Russian Federation and Ukrainian authorities," he said. "So far, two safe passage convoys have been successfully completed."
The first stage at the weekend saw 101 civilians safely evacuated to safety to the north of Mariupol, while the second phase on Wednesday night led to "more than 320" from the region finding a safe haven.
While a third operation is underway, Guterres would not provide any details until it is completed, "to avoid undermining possible success."
"It is good to know that even in these times of hyper-communications, silent diplomacy is still possible and is sometimes the only effective way to produce results," he said.
The UN chief said the United Nations will continue to scale up humanitarian operations to save lives and reduce suffering, and that he also discussed worldwide food security during his talks with both leaders.
"A meaningful solution to global food insecurity requires reintegrating Ukraine's agricultural production and the food and fertilizer production of Russia and Belarus into world markets, despite the war," he said.