Moscow and Kyiv have exchanged almost daily drone or missile attacks over the nearly three-year war, targeting energy and military sites in both countries.

Strikes have escalated after Donald Trump won last year's US presidential election, with the Republican seeking a swift end to the fighting.

"The most terrible thing happened as a result of a drone attack on a residential house -- a two-year-old child and his mother were killed," Vyacheslav Gladkov, the governor of Russia's Belgorod border region said on Telegram.

Another child and his father were also injured in the strike.

Russia's defence ministry said earlier it had downed 104 Ukrainian drones over western regions including Kursk and Bryansk, with smaller numbers intercepted over Smolensk, Tver, Belgorod and elsewhere.

Ukraine said one strike had hit an oil refinery in the town of Kstovo in Russia's Nizhny Novgorod region, around 800 kilometres (500 miles) from the front lines in eastern Ukraine.

Falling debris from a drone triggered a fire at the site, Russia said earlier.

"As a result of repelling a drone attack, debris fell on the Sibur-Kstovo enterprise causing a fire to break out," Sibur, a large petrochemical firm that owns the facility, said on Telegram.

Both Sibur and the regional governor said there were no casualties and firefighters were working to extinguish the blaze.

The governor of Russia's Smolensk region, Vasily Anokhin, also said a Ukrainian drone "was shot down during an attempted attack on a nuclear power facility," adding there was no damage or casualties.

The governor did not specify which facility, but the Smolensk nuclear power plant is located near the town of Desnogorsk.

Ukraine's military said Russia had also launched an overnight drone attack of its own, resulting in air alerts in multiple Ukrainian regions.

The Ukrainian air force said it had downed 29 Russian drones over nine mainly southern and eastern regions.

In Kyiv, Mayor Vitali Klitschko said debris from a Russian drone had fallen in a central district of the capital.

And in the southern Black Sea region of Odesa, the governor said Russian drones had attacked port facilities in the town of Izmail.

In the southern city of Kherson, mayor Roman Mrochko said a 52-year-old man had been fatally wounded in a Russian drone attack.

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