KHARKIV, Ukraine (Reuters) -A Russian strike on a crowded DIY hardware store in Kharkiv killed 12 people and wounded dozens more, Ukrainian prosecutors said on Sunday morning, the death toll rising as the country's second-largest city reeled from two attacks a day earlier.

Two guided bombs hit the Epicentr DIY hypermarket in a residential area of the city on Saturday afternoon, Regional Governor Oleh Syniehubov said on national television.

The strikes caused a massive fire which sent a column of thick, black smoke billowing hundreds of metres into the air.

Forty-three people were injured, the local prosecutors' office said, adding that ten of the twelve dead had still not been identified.

Kharkiv Mayor Ihor Terekhov said about 120 people had been in the hardware store when the bombs struck.

"The attack targeted the shopping centre, where there were many people - this is clearly terrorism," Terekhov said.

In a post on the Telegram app, Ukraine's Interior Minister Ihor Klymenko said 16 people were still missing after the strike.

The past week has seen an uptick in strikes on the city after Russian troops stormed across the border, opening a new front north of the city.

Russia has bombarded Kharkiv, which lies less than 30 kilometres (20 miles) from its border, throughout the war, having reached its outskirts in a failed bid to capture it in 2022.

President Volodymyr Zelenskiy issued a plea to Ukraine's Western allies to help boost air defences to keep the country's cities safe. French President Emmanuel Macron, writing on social media platform X, denounced the attack on the store as "unacceptable."

A separate early evening missile strike hit a residential building in the centre of the city of 1.3 million. The number of people wounded by that strike had climbed to 25 by Sunday morning.

The missile left a crater several metres deep in the pavement at the foot of the building, which also housed a post office, a beauty salon and a cafe.

Emergency workers ushered away residents of nearby apartment buildings. Some of the injured had blood on their faces.

Just over the border, in Russia's Belgorod region, the regional governor said four residents died in Ukrainian attacks on Saturday.

FIREFIGHTERS BATTLE BLAZE

Andriy Kudinov, director of the suburban shopping centre, told local media the hardware store was full of shoppers buying items for their summer cottages.

It took 16 hours to fully extinguish the fire at the centre, which had raged over an area of 13,000 square metres (15,548 square yards), Interior Minister Klymenko said.

Rescuers, medics and journalists occasionally had to rush away from the scene of both strikes on the city and take cover on the ground, fearing another strike, as has occurred during several recent Russian attacks.

Dmytro Syrotenko, a 26-year-old employee of the DIY centre, described panicked scenes.

"I was at my workplace. I heard the first hit and ... with my colleague, we fell to the ground. There was the second hit and we were covered with debris. Then we started to crawl to the higher ground," said Syrotenko, who had a large gash on his face.

Syrotenko told Reuters he was taken to safety by a rescue worker who helped him, several colleagues, and shoppers.

Zelenskiy, in his nightly video address, denounced the strike as "yet another example of Russian madness. There is no other way to describe it."

"When we tell world leaders that Ukraine needs sufficient air defences, when we say we need real decisive measures to enable us to protect our people, so that Russian terrorists cannot even approach our border, we are talking about not allowing strikes like this to happen," he said.

Writing later on Telegram, Zelenskiy noted air raid alerts had been in effect in Kharkiv for more than 12 hours and 200 emergency workers and 400 policemen remained at the scene dealing with the aftermath of the attacks.

Moscow denies deliberately targeting civilians, but thousands have been killed and injured during its 27-month invasion of Ukraine.

(Additional reporting by Olena Harmash; Editing by Ron Popeski, Bill Berkrot, David Gregorio, Chris Reese and Sonali Paul)