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. Russia denies targeting civilians.  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 neighboring Belarus took off. Reuters was unable to verify that information.  Britain's defense 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.  There is still no prospect of talks to end the war, now in its 11th month.  Ukrainian President Volodymyr Zelenskiy is vigorously pushing a 10-point peace plan that envisages Russia fully respecting Ukraine's territorial integrity and pulling out all its troops.  ‘Today’s realities’  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."  Zelenskiy addressed parliament behind closed doors on Wednesday, greeting members with "Glory to Ukraine", prompting the response: "Glory to heroes".  He said Ukraine has secured the release of 1,456 prisoners of war since Russia invaded on Feb. 24. Russia is thought to hold thousands of Ukrainian PoWs, but the exact figures are not known.  Russian forces abandoned Kherson city last month in one of Ukraine's most significant gains of the war. Kherson region, located at the mouth of the mighty Dnipro River and serving as gateway to Russian-annexed Crimea, is strategically important.  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, Zelenskiy'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. A baby's picture hung in an empty room and beds and hospital equipment stood empty and unused.  A Russian strike killed at least 10 people and wounded 58 in Kherson last Saturday, Ukraine said.  In Wednesday's report, Ukraine's General Staff also reported further Russian shelling in Zaporizhzhia region and in the Sumy and Kharkiv regions of northeast Ukraine.  Reuters was unable to verify the battlefield reports.  Pressure  "There has been very little change in terms of the front line but pressure from the enemy has intensified, both in terms of the numbers of men and the type and quantity of equipment," Ukrainian military analyst Oleh Zhdanov said.  Putin called his invasion of Ukraine a "special military operation" to demilitarize his neighbor, which he said posed a threat to Russia.  The war has caused the deaths of tens of thousands of Ukrainian civilians and service personnel on both sides, the devastation of Ukrainian cities and towns and the flight of millions from their homes. It has also disrupted the global economy, driving up energy and food prices.  Russian Prime Minister Mikhail Mishustin said on Wednesday that the country's economy, battered by Western sanctions, shrank by more than 2% over the past 11 months.  On Tuesday, Putin retaliated against a price cap of $60 per barrel of Russian oil imposed by the West on Dec. 5, saying Moscow would now ban oil sales to nations that implement it.  The cap, unseen even in the times of the Cold War between the West and the Soviet Union, is aimed at crippling Russia's military efforts in Ukraine - without upsetting markets by actually blocking its supply of oil.  Russia is the world's second-largest oil exporter after Saudi Arabia, and any actual disruption to its sales would have far-reaching consequences for global energy supplies.