Russian officials said on Thursday that Ukrainian saboteurs crossed into western Russia and attacked local villages, as the war extended into its second year.
Amid conflicting initial reports, Russia's Federal Security Service said fighting with the sabotage unit was taking place in the Bryansk region.
There was no immediate comment from Ukrainian officials, and the exact circumstances of the incident were unclear.
If confirmed, it would be another indication following drone attacks earlier this week that Kyiv could be taking the fight into Russian territory, exposing Russian defensive weaknesses, embarrassing the Kremlin and sowing unease among Russian civilians.
The Federal Security Service was quoted by the Russian state Tass news agency as saying that "activities to eliminate armed Ukrainian nationalists who violated the state border" were underway.
Tass, citing Russian law enforcement, reported earlier that the saboteurs were holding up to six people hostage. The local governor said the group had fired on a vehicle there, killing one man and wounding a 10-year-old.
Drones that the Kremlin said were launched by Ukraine flew deep inside Russian territory on Tuesday, including one that got within 100 kilometers (60 miles) of Moscow.
Thursday's apparent incursion was also embarrassing for Russian President Vladimir Putin, coming days after he ordered the Federal Security Service to tighten controls on Russia's border with Ukraine.
Tass reported, citing an unnamed security official, that two villages in the Bryansk region Sushany and Lyubechane were under attack by "several dozen armed fighters."
Alexander Bogomaz, the governor of the Bryansk region, which borders Ukraine, said the group fired on a vehicle in Lyubechane, killing one man and wounding a child. He also said that a Ukrainian drone struck a house in the Sushany, setting it ablaze.
In Ukraine on Thursday, three people were killed and six others were injured when a Russian missile hit a five-story apartment building in a southeastern city.
Ukrainian President Volodymyr Zelenskyy said several floors of the building were destroyed in the strike, which occurred while it was still dark.
The State Emergency Service said in an online statement that it had rescued 11 people so far.
Zaporizhzhia is a large city that had a population of more than 700,000 before Russia's full-scale invasion of its neighbor just over a year ago. It is the administrative capital of the partially occupied Zaporizhzhia region, which is home to Europe's largest nuclear plant.
Russian artillery, drones and missiles have pounded Ukrainian-held areas in the country's south and east for months. Moscow denies aiming at civilian targets, but its indiscriminate shelling has wrought wide destruction in urban centers.
The war largely slowed to a grinding stalemate during the winter months.
Zelenskyy said Russia "wants to turn every day for our people into a day of terror." He added: "But evil will not reign in our land."
Meanwhile, a fierce battle continued for control of Bakhmut, a key eastern stronghold where Ukrainian officials say they might strategically withdraw.
Ukraine's General Staff reported that the Russian forces "continue to advance and storm the city," but Kyiv's troops repelled some of the attacks on the ruined city. Donetsk regional Gov. Pavlo Kyrylenko reported one person was wounded in Bakhmut on Thursday morning.
Bakhmut was among cities and villages in the Donetsk region that came under Russian shelling, according to the General Staff update.
Taking the city could not only give the Russian forces a rare battlefield gain after months of setbacks but might rupture Ukraine's supply lines and allow the Kremlin's forces to press toward other Ukrainian strongholds in Donetsk.
Kyiv, March 2 (AP/PTI)