Moscow has warned of retaliation after an oil depot in the Russian city of Belgorod caught fire following what the regional governor said were air strikes by two Ukrainian helicopters.
The incident on Friday is the latest in a series of apparent Ukrainian attacks on Russian soil, which have raised concerns about an escalation of the conflict.
The Russian Defence Ministry said in a statement that two Ukrainian Mi-24 helicopters had crossed the border at low altitude and fired missiles at the depot. It said one helicopter was shot down by Russian air defences.
The Belgorod regional governor, Vyacheslav Gladkov, said the fire at the oil depot had been extinguished and there were no casualties. He said two people had been injured in the attack.
The Russian Foreign Ministry said the attack was a .
