-A Russian regional official said on Wednesday that frontier guards in the Kursk region bordering Ukraine had come under fire, while schools in nearby Belgorod were evacuated after a bomb threat, according to the city's mayor.
Moscow, which sent thousands of troops into Ukraine on Feb. 24 in what it called a "special military operation", has accused Ukraine of attacking Russian targets across the border.
"Yesterday ... they tried to fire mortars at the position of our border guards in the Sudzhansky district," said Roman Starovoit, the governor of the Kursk region.
"Russian border guards returned fire ... There were no casualties or damage on our side."
Reuters could not immediately verify the report.
Kremlin spokesman Dmitry Peskov said he did not yet have details of the incidents in the two Russian regions, but described the reports as "serious".
In response to a question about the border incident, a spokesman for the general staff of Ukraine's armed forces said: "We do not have such information."
Starovoit said officials were in touch with the defence ministry and urged citizens to remain calm. In separate comments to the RIA news agency, he said the mortars fired at the Sudzha border crossing had not reached Russian territory.
The mayor of the Russian city of Belgorod, some 35 km (22 miles) from the border with Ukraine, said schools had been evacuated after receiving bomb threats.
"We understand that this is part of the information pressure (campaign) against our region," mayor Anton Ivanov said, without saying who he thought was responsible for the threats.
Russia last week accused Ukrainian military helicopters of carrying out an air strike against a fuel depot in Belgorod, one of Russia's main logistics hubs for its military campaign in Ukraine. A senior Ukrainian official denied responsibility.
The Kremlin said at the time that the incident did not create comfortable conditions to continue peace talks with Kyiv.