Russian forces stepped up mortar and artillery attacks on the recently liberated city of Kherson in southern Ukraine on Wednesday, Ukraine’s military said, while also exerting pressure along frontlines in the east.

Russia fired 33 missiles from multiple rocket launchers at civilian targets in Kherson in the 24 hours to early Wednesday, the General Staff of Ukraine’s Armed Forces said in its morning report.

Heavy fighting also persisted around the Ukrainian-held city of Bakhmut, now largely in ruins, in the eastern province of Donetsk, and to its north, around the cities of Svatove and Kreminna in Luhansk province, where Ukrainian forces are trying to break Russian defensive lines.

Air raid sirens also sounded across Ukraine on Wednesday morning, officials said, though there were no reports of any missile strikes and the all-clear was later given. Ukrainian social media reports said the nationwide alert may have been declared after Russian jets stationed in neighbouring Belarus took off.

Britain’s defence ministry said in its update on Ukraine that Russia had likely reinforced the Kreminna section of the frontline as it is logistically important to Moscow and has become relatively vulnerable following Ukrainian advances further west.

Ukrainian President Volodymyr Zelensky is vigorously pushing a 10-point peace plan that envisages Russia fully respecting Ukraine’s territorial integrity and pulling out all its troops.

But the Kremlin on Wednesday rejected the plan, reiterating its stance that Kyiv must accept Russia’s annexation — announced in September after “referendums” rejected by Ukraine and most other nations — of four Ukrainian regions: Luhansk and Donetsk in the east, and Kherson and Zaporizhzhia in the south.

“There can be no peace plan for Ukraine that does not take into account today’s realities regarding Russian territory, with the entry of four regions into Russia,” Kremlin spokesman Dmitry Peskov said. ”Plans that do not take these realities into account cannot be peaceful.”

Zelensky addressed the parliament behind closed doors on Wednesday, greeting members with “Glory to Ukraine”, prompting the response: “Glory to heroes”.

He said Ukraine had secured the release of 1,456 prisoners of war since Russia invaded on February 24. Russia is thought to hold thousands of Ukrainian PoWs, but the exact figures are not known.

The joy of Kherson residents over the city’s liberation has quickly given way to fear amid relentless Russian shelling from the east bank of the Dnipro, and many have since fled.

Russian forces shelled the maternity wing of a hospital in Kherson, Kyrylo Tymoshenko, Zelensky’s deputy chief of staff, said on Telegram. No one was hurt and the staff and patients had been moved to a shelter, he added.

TV footage showed workmen replacing shattered windows with sheets of board amid the rubble of damaged brick walls.