A group of Ukrainian combatants crossed into the southern Bryansk region, in Russia and committed a “terrorist attack”, Russia said on Thursday.

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”. The reports were not confirmed by western news outlets.

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.