Russia on Thursday reported that a group of Ukrainian combatants had crossed into the southern Bryansk region, with the Kremlin calling it a "terrorist attack".

Moscow said that it was deploying security services and the military to "destroy" the group and that President Vladimir Putin was being kept "constantly" updated.

Ukraine dismissed the reports, calling them a "provocation". AFP could not independently verify them.

Kremlin spokesman Dmitry Peskov said there had been "an attack by Ukrainian fighters".

"We are talking about a terrorist attack," he noted.

Putin had been due to visit the southern Stavropol region for a meeting on education but will hold a video call instead, he said.

The FSB security service said in a statement carried by Russian news agencies that the incident happened in the Klimovsky district in the Bryansk region, which borders Ukraine.

"The FSB of Russia and forces of the Russian defence ministry are taking measures to destroy armed Ukrainian nationalists who have infiltrated the state border," the statement said.

Russian response

Earlier in the day the regional governor said that a reconnaissance group had crossed into southern Russia and opened fire, and that the military was responding to "eliminate" the group.

"A reconnaissance and sabotage group penetrated from Ukraine to the Klimovsky district in the village of Lyubechane," the Bryansk regional governor, Alexander Bogomaz, said in a statement.

"The Russian armed forces are taking all the necessary measures to eliminate the sabotage group" in the Bryansk region.

Bogomaz added that members of the alleged Ukrainian sabotage group had opened fire on a moving car and that one person was killed and a 10-year-old had been wounded.

"The child has been taken to the hospital, he is receiving all the necessary assistance," Bogomaz said on Telegram.

Russian news agencies, citing sources in law enforcement and the emergency services, said members of the group may have taken hostages.

Bogomaz also said that a Ukrainian drone had attacked the village of Sushany, leaving a residential home in flames, and that mortar fire had damaged two homes in Lomakovka, also in Bryansk region.

The governor of another Russian border region, Kursk, Roman Starovoyt, said Ukrainian shelling on the village of Tetkino had left one dead and one injured.

He said the shelling damaged three houses and cut power in the village.

Russian officials say regions bordering Ukraine are routinely shelled by Ukrainian forces but the infiltration, if confirmed, would be a rare instance of fighting inside Russia.