Ukrainian President Volodymyr Zelensky has said that an alleged Russian agent involved in the attack on the city of Kramatorsk will be charged with treason.
He said those who help Russia destroy lives deserve the “maximum punishment”.
Eleven people, including three teenagers, were killed in a missile attack on Tuesday on a popular restaurant.
Ukrainian security services said the man sent video footage of the restaurant to the Russian army hours before it was destroyed.
Among the dead were 14-year-old twin sisters Yulia and Anna Aksenchenko and a 17-year-old girl.
“The Russian missiles stopped the beating of two angels’ hearts,” the education department of the Kramatorsk City Council said in a statement.
At least 60 others were injured, including Colombian citizens and a prominent Ukrainian writer.
On Wednesday, the Ukrainian security services published a photo of a local man they had arrested, calling him a Russian agent.
Speaking in his evening address, Mr. Zelensky made it clear that the country’s security services worked hand-in-hand with police special forces to arrest the suspect – who could face life in prison.
Emergency services said on Wednesday that search and rescue efforts were continuing.
Kramatorsk, the eastern city in the Donetsk region, is under Ukrainian control but is close to the Russian-occupied parts of the country.
In April last year, more than 50 people were killed and many more injured in a missile attack on a train station in the city.
The Ria Lounge, which was targeted this time, was a popular spot that regularly hosted international journalists, volunteers and Ukrainian soldiers taking a break from the nearby front lines.
Sergio Jaramillo Caro, a former Colombian peace negotiator, told the BBC he was sitting in the restaurant when it was attacked on Tuesday night, but only suffered minor injuries.
Mr Jaramillo Caro described the moments after the explosion, saying he saw “particles moving in slow motion” as he tried to make sense of what was going on.
A prominent Ukrainian writer sits with them – her identity has not been revealed – in critical condition and “fighting for her life”.
“Please pray for her,” Mr. Jaramillo Caro said.
Valentina, a Kramatorsk resident who owns a cafe near the site, spoke of the damage after the attack. “Everything there was blown away,” she told Reuters news agency, adding that “no glass, windows or doors were left.”
The Kremlin again claimed it had only carried out strikes on military targets, and the Russian Defense Ministry claimed it had destroyed a “temporary deployment of Russia’s armed forces.” [Ukrainian] Leaders ”in Kramatorsk, without going into details.
Yuriy Sak, an adviser to Ukraine’s defense ministry, told the BBC that Ukraine’s air defenses were “currently insufficient to cover the entire territory of Ukraine”.
Ukraine continues to demand that its allies provide them with modern combat aircraft to help it defend itself from Russian strikes.
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