Ukraine's President Volodymyr Zelenskiy confirmed for the first time on Monday that Ukrainian troops have been active in Russia's Belgorod region as they seek to protect Ukrainian towns near the border.
Ukrainian troops remain in parts of the neighbouring Russian region of Kursk eight months after a cross-border incursion, though Russian forces have recaptured much lost territory.
In his nightly video address, Zelenskiy said Ukraine's top commander, Oleksandr Syrskyi, had presented a report "on the front line, our presence in the Kursk region and our presence in the Belgorod region."
"We continue active operations in the enemy's border areas and this is absolutely justified. The war must return to where it came from.
"Our main objective remains the same: to protect our land and our communities in the Sumy and Kharkiv regions from Russian occupiers."
President 
