Russia on Monday began evacuating civilians in a second border region as Ukraine continued its surprise offensive inside the country.
Kyiv increased activity near the border just days after its biggest incursion into Russian territory since 2022.
A Russian official said 11,000 people in the Belgorod region have been told they must leave their homes because of military action.
District administration head Andrey Miskov said on social media that residents were moved on buses headed for temporary accommodation.
Around 500 people remain, he said.
The entire region is reportedly under a missile alert amid the threat from Ukrainian troops.
Ukrainian forces rammed through the Russian border last Tuesday, sweeping across some Western parts of Russia's Kursk region and advancing up to 18 miles.
It is the deepest incursion into Russia since Moscow launched its full-scale invasion of Ukraine in February 2022.
Apparently caught by surprise, Russia by Sunday had stabilised the front in the Kursk region, though Ukraine had carved out a sliver of territory where battles were continuing on Monday, according to Russian war bloggers.
President Volodymyr Zelensky said the incursion into Russian territory was to "restore justice" and pressure Moscow's forces.
In the neighbouring Belgorod region to the south, regional governor Vyacheslav Gladkov said evacuations had begun from the Krasnaya Yaruga District due to "enemy activity on the border".
"I am sure that our servicemen will do everything to cope with the threat that has arisen," Mr Gladkov said.
"We are starting to move people who live in the Krasnaya Yaruga district to safer places."
Vladimir Putin’s army has imposed a tight security regime in the Kursk, Bryansk and Belgorod regions.
Its ally Belarus said it was bolstering its troop numbers at its border after Minsk said Ukraine had violated its airspace with drones.
Russian officials claim Ukraine's attacks on Russian sovereign territory are aimed at showing its Western supporters that Kyiv can still muster major military operations while trying to gain a bargaining chip ahead of possible ceasefire talks.
Five Ukrainian drones were destroyed over Belgorod overnight, 11 over Kursk and two over Voronezh, according to Russia's defence ministry, which said it was repelling Ukrainian attacks inside Russia.
It listed considerable heavy weaponry including tanks which it said it had destroyed.
