KYIV, Ukraine, Dec 29 (AFP) - Air raid sirens rang across Ukraine as Russia unleashed more than 100 missiles on Thursday morning, according to a Ukrainian presidential adviser, and blasts were heard in several cities, including the capital Kyiv."A massive air raid. More than 100 missiles in several waves," presidential office adviser Oleksiy Arestovych wrote on Facebook, and the head of Ukraine's Mykolaiv region also reported Russian missiles in the air.

Explosions were heard in Kyiv, Zhytomyr and Odesa, according to a Reuters correspondent and local media reports.

Power cuts were announced in the Odesa and Dnipropetrovsk regions, aimed at minimising potential damage to the energy infrastructure.

The blitz came hard on the heels of the Kremlins rejection of a Ukrainian peace plan, insisting that Kyiv accept Russia's annexation of four regions.

Moscow has repeatedly denied targeting civilians, but Ukraine says its daily bombardment is destroying cities, towns, and the country's infrastructrure from power to medical.

On Wednesday, Russian shelling hit the maternity wing of a hospital in the city of Kherson, 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."

Ukraine's recently liberated southern city of Kherson has remained under constant 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.

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.

Sweeping sanctions have been imposed on Russia for the war, which has killed tens of thousands of people, driven millions from their homes, left cities in ruins and shaken the global economy, driving up energy and food prices.

Russian gas exports to Europe via pipelines collapsed to a post-Soviet low in 2022 as its largest customer cut imports due to the Ukraine conflict and a major pipeline was damaged by mysterious blasts, Gazprom data and Reuters calculations show.