A shell hit a temporary Russian military camp near the border with Ukraine late on Tuesday, Tass news agency said and cited a source as saying preliminary data showed it had been fired from the Ukrainian side.

Tass issued the report shortly after a senior local official reported a series of explosions outside the city of Belgorod, close to the border with Ukraine.

Video posted online from two local Belgorod news outlets appeared to show ammunition blowing up in the distance but Reuters was not immediately able to confirm this was the case.

Tass cited an emergency services source as saying four people had been injured in the blast.

Belgorod governor Vyacheslav Gladkov earlier said in an online post that the blasts occurred near the village of Krasny Oktyabr, about 30 km (19 miles) southwest of Belgorod. He did not give a reason for the blasts and promised an update later.

Belgorod is 80 km (50 miles) north of the Ukrainian city of Kharkiv, which Russian forces have bombarded heavily in recent weeks.