The incident came as Ukraine prepares for a counter-offensive against Russia's invading forces.
The respected Russian news outlet Kommersant reported on Saturday that a Russian raiding party comprising an Su-34 fighter-bomber, an Su-35 fighter and two Mi-8 helicopters had been shot down in an ambush near Klintsy in Russia's Bryansk region.
It said they had been due to attack targets in the Chernihiv region of Ukraine, directly over the border.
The Russian state news agency TASS said on Saturday that a Russian Su-34 warplane had crashed, but did not specify a cause, and cited emergency services as saying an engine fire had brought down a helicopter.
It did not mention the Su-35 or a second helicopter, although several heavily followed Russian pro-war military bloggers also said the four aircraft had been shot down.
The Pul Pervovo Telegram channel, a Belarusian state outlet that reports on Lukashenko's activities, said on Monday that he had visited an air force command base, and quoted him as saying:
"Three days after the events near us - I mean in the Bryansk region, when four aircraft were shot down. We are forced to respond. Since then, we, our troops, have been on high alert."
Lukashenko's reported visit to the base was his first public appearance in almost a week, following speculation over the health of the 68-year-old leader.
Exiled Belarusian opposition leader Sviatlana Tsikhanouskaya told her supporters on Monday to be ready to grab any chance to turn her country into a democracy as speculation about the health of veteran President Alexander Lukashenko swirled.
It was shortly after her message to supporters via Twitter, a Belarusian state news channel released a photo of Lukashenko at what it said was a military command centre in what would be his first public appearance in almost a week.
State TV later broadcast a clip of Lukashenko at what it said was a central air force command base. It showed him sitting in a chair talking to officers. Dressed in a military uniform, Lukashenko appeared to have a bandage on his left hand and to be short of breath at times.
Lukashenko, who once told Reuters he was "the last and only dictator in Europe", has ruled Belarus with an iron first since 1994, using his security forces to intimidate, beat and jail his opponents or force them to flee abroad.
A staunch ally of Russia, Lukashenko before Monday had not been pictured in public since May 9 when he reviewed Russia's annual military parade on Moscow's Red Square as a guest of President Vladimir Putin.
Looking tired and a little unsteady, Lukashenko was seen with a bandage on his right hand at the time. He skipped a lunch hosted by Putin. He also swerved his traditional post-parade stroll and was driven a short distance to an event instead.
Speculation about his health intensified on Sunday when Lukashenko missed a ceremony in Minsk amid unconfirmed media reports that he had been hospitalised. His place was taken by Prime Minister Roman Golovchenko. Lukashenko's office has declined to comment on his absence.
A truculent but long-standing ally of Moscow, Lukashenko has become more dependent on Russia for energy and loans since the Russian invasion of Ukraine last year, when he allowed Russian forces to use his country as a launch pad for what Moscow called its "special military operation."
