Russia said on Thursday it had repelled more cross-border attacks from Ukraine while its aerial assaults on Kyiv killed another three people including a nine-year-old girl and her mother locked out of an air raid shelter.

Both sides are trying to sap morale and weaken military capacity ahead of a long-promised Ukrainian counter-offensive against Russia's 15-month-old incursion.

The war has killed tens of thousands, shattered Ukrainian cities and brought increasing attacks on Russian soil.

Russia's defence ministry said it had repelled three cross-border attacks on Thursday near the town of Shebekino, and it accused Ukraine of using what it said were "terrorist formations" to carry out attempted attacks on Russian civilians.

"The selfless actions of Russian servicemen repelled three attacks by Ukrainian terrorist formations," the Russian ministry said. "No violations of the state border were allowed."

The Russian Volunteer Corps (RVC), a far-right paramilitary group of ethnic Russians that supports Ukraine, claimed to be fighting inside Russia. "The second phase promised by the RVC's commander has begun!" it said on Telegram, referring to a previous incursion, alongside images of fighters firing weapons and inside a building.

Ukraine denies its military is involved in the incursions into Russia's Belgorod border region and says they are conducted by Russian volunteer fighters.

Moscow accuses Ukrainian "terrorists" of targeting Russia's western border. Russian officials say the group of fighters is a proxy run by Ukraine.

In Kyiv, Ukraine said it shot down 10 ballistic and Iskander cruise missiles in Russia's 18th attack on the capital since the start of May. But a nine-year-old girl, her mother and another woman died when debris fell near an air raid shelter they had been trying to enter.

"The entrance was closed, there were already maybe five to 10 women with children," resident Yaroslav Ryabchuk said. "They knocked loudly enough ... They tried to enter the shelter, no one opened up for them. My wife died." (Reuters)