UNITED NATIONS, May 28 (Xinhua) -- UN Secretary-General Antonio Guterres on Thursday called for immediate and sustained de-escalation of the Ukraine conflict.

Speaking at a Security Council meeting on Ukraine following Russia's massive strikes across Ukraine over the weekend, Guterres said the direction of the conflict risks getting out of control.

He warned of the risk of miscalculation and escalation with unknown and unintended consequences. "Let's speak plainly. The current course is not sustainable. This trajectory must change. The death spiral must stop," said Guterres.

Since February 2022 when the conflict broke out, more than 15,000 civilians have been killed in Ukraine, with nearly 800 children among them. Reports from Russia indicate a growing number of civilian casualties, including children, he said.

The front line is virtually frozen with swarms of drones inflicting heavy casualties. Civilian infrastructure is being destroyed on a vast scale, especially energy infrastructure, said Guterres.

"What is needed now is de-escalation -- immediate and sustained. What is needed now is a full and unconditional ceasefire. What is needed now is more diplomacy. What is needed is to create the conditions for a just, lasting and comprehensive peace -- in line with the Charter of the United Nations, international law, and UN resolutions," he said. "The choice is clear. The responsibility is clear. The time for peace is now."

Russian Defense Ministry said Sunday that the Russian military carried out a series of missile and drone strikes against Ukrainian military targets in retaliation for Ukraine's "attacks against civilian targets on Russian territory."