Russia's security service said on Thursday that a border post in the Bryansk region had been fired at with mortars from Ukraine in the latest of a series of reported cross-border attacks that Moscow has said may trigger an escalation of the conflict.
No one was injured in the incident but some vehicles were damaged, a spokesman for Russia's FSB security service told state television.
Ukraine's defence ministry and military did not immediately respond to requests for comment.
Ukrainian interior ministry adviser Anton Herashchenko said in a post on the Telegram messaging service that something "fell and caught fire" at a military facility in Bryansk near the border.
The post mocked Russia for immediately blaming Ukraine, but did not explicitly deny Ukraine was responsible.
Russia has reported a series of attacks on border areas by Ukrainian forces in recent weeks, including by a strike on a fuel depot in the city of Belgorod earlier this month.
On Wednesday Russia's defence ministry said the continuation of "sabotage and attacks" by Ukrainian forces could trigger strikes on Kyiv.
"If such incidents continue, then consequence from the armed forces of the Russian Federation will be attacks on decision making centres, including in Kyiv, which the Russian army has refrained from to date," the defence ministry said.
Authorities in four Russian regions bordering Ukraine and in Russian-controlled Crimea announced they were stepping up security measures on Monday over what they said were "possible provocations" from the Ukrainian side.
After the mortar attack, a number of schools in the area closed, Russia's TASS news agency reported.
Moscow's incursion into Ukraine, the biggest attack on a European state since 1945, has seen more than 4.6 million people flee abroad, killed or wounded thousands and left Russia increasingly isolated on the world stage.
The Kremlin says it launched a "special military operation" to demilitarise and "denazify" Ukraine. Kyiv and its Western allies reject that as a false pretext for an unprovoked attack.
(Reporting by Conor Humphries in Dublin; editing by Guy Faulconbridge)
