"Russian missiles hit the Nova Poshta centre - an ordinary civilian object," President Volodymyr Zelenksyy said on the Telegram messaging app.

He posted a video showing a building with windows blown out and construction materials strewn about, with red trucks labelled Nova Poshta in Ukrainian.

The governor of the Kharkiv region, Oleh Synehubov, said several of the injured were in serious condition in hospital.

Those killed and injured were employees of the postal centre, Mr Synehubov said.

Police said the workers did not have time to run to the shelter because the siren sounded a second before impact.

The reports have not been independently verified and there has been no immediate comment from Russia.

Both sides have denied targeting civilians in the course of the war.

Kharkiv, Ukraine's second-largest city, was devastated in the early days of Russia's full-scale invasion.

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Elsewhere across the country, at least three civilians have been killed and others wounded as Russian forces continue their shelling.

A man died as Russian forces shelled the Ukrainian-held town of Nikopol from their stronghold at the Zaporizhzhia nuclear power plant, according to Ukrainian local governor Serhii Lysak.

He said emergency services in Nikopol were working to assess the damage.

In Kryvyi Rih, the central Ukraine hometown of President Zelenskyy, a 60-year-old man died on Friday evening when a Russian missile hit an industrial facility, according to Telegram posts by mayor Oleksandr Vilkul.

The man's wife was in hospital with serious shrapnel wounds, Mr Vilkul said.

Russian missiles and drones hit the same place again overnight, causing unspecified damage and sparking a fire that was put out by morning.

Nobody was hurt in the second strike.

Russian Defence Ministry spokesman Igor Konashenkov told reporters that Russian forces had destroyed the Ukrainian military's fuel and ammunition depots near Kryvyi Rih's local airport.

Ukrainian officials have not yet responded to Mr Konashenkov's claim.

In southern Ukraine's Kherson region, one civilian was killed and another wounded during "mass shelling" attacks by Russian troops, governor Oleksandr Prokudin said on Saturday.

"The Russians used mortars, artillery, tanks, drones, and multiple-rocket launchers to target the region, striking some residential areas", Mr Prokudin wrote on Telegram.

Russian shelling over the past day also wounded one civilian in the frontline city of Avdiivka, in Ukraine's eastern Donetsk region, acting local governor Ihor Moroz said.

Avdiivka has been fiercely contested by Russian and Ukrainian forces in recent weeks as Kyiv's forces try to hold off a renewed Russian assault.