A Russian strike on Thursday killed at least 51 people gathered for a wake in an eastern Ukrainian village in what a UN official called a "horrifying" attack. 

Footage published by the Ukrainian police showed a large area of smoking rubble and several bodies being taken away by emergency workers in the village of Groza.

Ukrainian President Volodymyr Zelensky posted an image of a woman kneeling over the body of someone apparently killed in the strike, with other corpses around her.

The mourners were in a cafe and there were also victims in a shop in the same building in the village, which has a population of 330 people, in the northeastern region of Kharkiv.

"A memorial service for a deceased fellow villager was being held," Interior Minister Igor Klymenko said on TV.

He said a six-year-old child was among the victims, adding that a total of 60 people had been attending the wake.

Groza is located more than 30 kilometres (18 miles) from the frontline town of Kupiansk in an area where Russian forces have been pushing to recapture territory they lost to Ukrainian troops last year.

Klymenko said initial evidence showed an Iskander missile had been used.

"The search and rescue operation is ongoing," Klymenko said. "There may still be people under the rubble".

Zelensky, who was attending a European summit in Spain, condemned the attack on social media.

He called the strike "completely deliberate" and said it was a "brutal Russian crime".

Defence Minister Rustem Umerov said Ukraine needed more air defence "to protect our country from terror".

"We are discussing this with partners," he wrote on social media, repeating Ukrainian calls for more protection against the daily barrages of drone and missile strikes.

- 'True evil' -

Denise Brown, Ukraine coordinator for the UN Office for the Coordination of Humanitarian Affairs(OCHA), also condemned the alleged Russian strike.

Brown said she was "appalled", adding that the images from the scene of the strike were "absolutely horrifying".

"Intentionally directing an attack against civilians or civilian objects is a war crime," she said in a statement.

A spokeswoman for the regional assembly quoted by Ukrainian media said it was the single most deadly attack since the start of Russia's invasion on February 24, 2022.

The head of the Kharkiv region Oleg Sinegubov said the strike took place around 1:15 pm (1015 GMT).

Regional authorities had recently ordered mandatory evacuations in the area after an uptick in Russian strikes.

Large swathes of the Kharkiv region were captured by Russian forces in the early days of their invasion launched in February last year.

Ukrainian forces recaptured much of the border territory during a lightning offensive late last year, but the regional capital, also called Kharkiv, still comes to regular shelling.

Zelensky's advisor Mykhailo Podolyak said the attack had "no military logic".

"This is a reminder to anyone who is willing to smile and shake hands with war criminal Putin at international conferences," he said, referring to Russian leader Vladimir Putin.

"A reminder to all those who want to sell something to Russia and return to bloody business as usual," he said, adding: "Putin's Russia is a true evil".

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