Russia said on Friday it had opened a criminal investigation into alleged Ukrainian shelling of a Russian border region in which it said people had been killed and wounded.
The state Investigative Committee did not specify the number of casualties in Thursday's incident, in which it said shells fired from Ukraine had destroyed an ammunition depot in the Belgorod region.
Russian officials also accused Ukraine on Thursday of strikes on border regions that hit a school, an apartment block and an electricity substation.
A Ukrainian official said the damage to the apartment block was caused by a stray Russian missile launched towards Ukraine. Reuters could not independently verify the assertions by either side.
The governor of Belgorod region, Vyacheslav Gladkov, said train operations had been suspended early on Friday near the town of Novyi Oskol after remains of a missile fell near the railway..
Russia's border regions have accused Ukraine of attacking targets including power lines and fuel and ammunition stores since Russia invaded its neighbour on Feb. 24.
Ukraine has not claimed responsibility, but an official has described previous incidents as "karma" for Moscow's invasion.
The war, which Moscow calls a "special military operation" to disarm and "denazify" its southern neighbour, has killed thousands of Ukrainians and left cities, towns and villages in ruins.
Ukraine and its Western allies have accused Russian forces of war crimes and targeting civilians, charges Moscow rejects.
