Ukraine's recently liberated southern city of Kherson suffered intense mortar and artillery attacks from Russian forces across the Dnipro river, while the Kremlin rejected a Ukrainian peace plan, demanding that Kyiv accept its annexation of four regions.

Kherson has remained under bombardment from Russian forces which had retreated to the east bank of the river when the city was retaken in a major victory for Ukraine last month.

On Wednesday, the shelling hit the maternity wing of a hospital, though no-one was hurt, according to Kyrylo Tymoshenko, President Volodymyr Zelenskiy's deputy chief of staff. Staff and patients were moved to a shelter, Tymoshenko said in a post on Telegram.

"It was frightening ... the explosions began abruptly, the window handle started to tear off ... oh, my hands are still shaking," Olha Prysidko, a new mother, said. "When we came to the basement, the shelling wasn't over. Not for a minute."

Moscow has repeatedly denied targeting civilians.

Zelenskiy, in a video address, urged Ukrainians to hug loved ones, tell friends they appreciate them, support colleagues, thank their parents and rejoice with their children more often.

"We have not lost our humanity, although we have endured terrible months," he said. "And we will not lose it, although there is a difficult year ahead."

Russia invaded Ukraine on Feb. 24. Kyiv and its Western allies have denounced Russia's actions as an imperialist-style land grab. Russian President Vladimir Putin calls it a "special military operation" to demilitarize its neighbour.