Russia said 14 people including two children had been killed and 108 injured in "indiscriminate" Ukrainian strikes allegedly including cluster bombs on the nearby Russian provincial capital of Belgorod on Saturday, and vowed to retaliate.
The Kommersant newspaper cited a source close to the Russian Investigative Committee as saying missiles fired from a multiple rocket launcher in Ukraine's Kharkov region had hit a skating rink on the central Cathedral Square, a shopping centre, residential buildings and a car.
No official comment was immediately available from Kyiv, but the Ukrainian news outlet RBC-Ukraine quoted sources as saying Ukrainian forces had struck military targets in Belgorod in response to a massive Russian bombardment of Ukrainian cities the previous day.
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Foreign Ministry spokeswoman Maria Zakharova told the state-run RIA news agency that Russia had requested a meeting of the UN Security Council to discuss the incident.
Air raid sirens had sounded around the city as regional governor Vyacheslav Gladkov urged all residents to move to shelters.
The Belgorod region, which adjoins northern Ukraine, has like other Russian border zones suffered shelling and drone attacks all year that authorities have blamed on Ukraine.
"Today, the Kyiv regime attempted an indiscriminate combined strike on the city of Belgorod with two 'Olkha' missiles in a banned cluster configuration, as well as Czech-made Vampire rockets," the Defence Ministry said in a Telegram posting. "This crime will not go unpunished."
It said most of the rockets including both 'Olkha' missiles had been shot down, averting far greater casualties, although fragments had fallen on the city.
Images posted by RIA showed at least three cars on fire, and other images posted online showed black smoke rising from the city.
Two residents told Reuters they had seen air defence missiles rising into the sky followed by explosions in the air and then louder blasts.
Russia unleashed its biggest air attack of the war on Friday. Ukrainian officials said 39 civilians had been killed and 159 wounded as Russia launched 158 missiles and drones at cities and towns across Ukraine.
Alexander Bogomaz, governor of the Bryansk region which also adjoins Ukraine, said on Saturday a child had been killed in strikes on "civilian objects" in two villages, without specifying when the attacks took place.
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