There have been reports of explosions over Belgorod, a Russian city near the Ukrainian border where Kyiv's soldiers have previously been accused of targeting military targets.
On social media, night footage with the sound of explosions and car alarms was shared. Although this has not been confirmed, users said that air defense systems were deployed during Tuesday's blasts.
"A loud bang, similar to the sound of an explosion of medium strength, was heard in the center of Belgorod," Russian news agency RIA Novosti said.
One person was hurt Monday in a fire at a Russian defense ministry facility in the city, about 20 miles from the Ukrainian border. A series of explosions were also reported.
However, regional governor Vyacheslav Gladkov refuted speculation that Monday's explosions were the result of Ukrainian forces, saying on his Telegram channel that Russia's "military aviation carried out combat missions as part of a special military operation," referring to the official Russian description of the Ukraine war.
He has yet to make a statement about the recent incidents. Newsweek has sought comment from the Russian and Ukrainian defense ministries.
Belgorod has been the target of claimed Ukrainian strikes in the past. Russia accused Ukraine last month of attacking a city's fuel store with a helicopter, shelling towns, and shooting missiles at an ammo stockpile.
Kyiv has claimed culpability. However, Russian state news agency Interfax reported that the Ukrainian side had launched repeated attacks on the Belgorod region since the war began, causing damage to more than 200 buildings.
Other Russian districts bordering Ukraine have also reported cases of cross-border shelling since Vladimir Putin's invasion began on February 24.
Last week, explosions were heard in Kursk, with a video purporting to show the blasts being shared on social media.
Additionally, two oil depots in the city of Bryansk in southwestern Ukraine are alleged to have been attacked by Ukrainian missiles. Meanwhile, Russian air defenses were deployed in response to an attack on a military airbase in the Voronezh region, which resulted in the hearing of two large explosions.
Moscow has responded sharply to British armed forces minister James Heappey's remarks that it was "legitimate" for Kyiv's soldiers to target Russian infrastructure.
The instances indicate that the Ukraine war may spill over the border. According to journalist Michael Weiss, "war is reaching Russia's homes, it's no longer just a TV war for them."