Ukraine's President Volodymyr Zelensky 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 neighboring Russian region of Kursk eight months after a cross-border incursion, though Russian forces have recaptured much lost territory.
In his nightly video address, Zelensky 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."
He later referred to operations in the area by Ukraine's 225th Assault Regiment and congratulated the unit for its performance.
Zelensky repeated Kyiv's long-held contention that despite Russia's recapture of areas of Kursk in recent weeks, the operation was successful in that it drew Russian forces away from the war's main front line in Ukraine's Donetsk region.
"Due to the entire Kursk operation, we have managed to reduce pressure on other frontline sectors, particularly in Donetsk region," he said.
The president last month referred obliquely to "certain steps" undertaken by Ukraine's military in Russia "a little below the Kursk region," implicitly suggesting a presence in Belgorod region.
Russian military bloggers had reported battles in Belgorod region between Russian and Ukrainian troops.
On Sunday, Russia said its troops had seized the village of Basivka in Ukraine's northeastern Sumy region - opposite Kursk - and were battering Ukrainian forces in different settlements.
Russian President Vladimir Putin has repeatedly suggested that Russian forces carve out a buffer zone along the border.
A Ukrainian military spokesperson issued a new denial on Monday that Basivka was in Russian hands.
Zelensky says Chinese men captured fighting for Russia in Ukraine
Ukrainian forces engaged six Chinese troops in battle in eastern Ukraine and took two soldiers prisoner, Zelensky said on Tuesday.
Speaking to reporters in Kyiv, he added that he had ordered Ukrainian officials to obtain an official explanation from China, which he described as having joined Russia's war against Ukraine, and that he expected the United States to react.
Beijing is a close ally of Moscow but is not publicly known to have directly aided in the Kremlin's full-scale invasion.
Writing on X, where he posted a video of one of the men, Zelensky said Kyiv has "information suggesting that there are many more Chinese citizens in the occupier's units" and that he had ordered officials to obtain a response from Beijing.
The Chinese foreign ministry did not immediately respond to a Reuters request for comment.
Zelensky did not say whether Ukraine believed the men were operating on Beijing's orders.
"Russia's involvement of China, along with other countries, whether directly or indirectly, in this war in Europe is a clear signal that Putin intends to do anything but end the war," Zelensky wrote.
He added that the captured men had documents confirming their identification, and added that Ukrainian intelligence and security officials were currently "verifying all the facts."
Kyiv summons China's diplomat over Chinese citizens fighting in Ukraine
Ukraine on Tuesday summoned China's charge d'affaires after Kyiv's troops took prisoner two Chinese citizens fighting in the eastern front, Ukraine's foreign minister said.
"Chinese citizens fighting as part of Russia's invasion army in Ukraine puts into question China's declared stance for peace and undermines Beijing's credibility as a responsible permanent member of the UN Security Council," Andrii Sybiha said on X.