The head of Russia's feared Wagner private army suggested Sunday that four Russian military aircraft that reportedly crashed in a region that borders Ukraine may have been shot down by Russia's own forces.

Russian officials have not commented on reports in Russian conventional and social media that two fighter planes -- an Su-34 and an Su-35 -- and two military Mi-8 helicopters crashed in the Bryansk region on Saturday.

State news agency Tass cited unspecified emergency services sources as saying the Su-34 and one helicopter crashed. Other sources, including Vladimir Rogov, the head of a Russian collaborationist organization in Ukraine's Zaporizhzhia province, claimed four aircraft went down.

All of them reportedly belonged to the same military air group.

During the war, cross-border shelling has repeatedly hit Bryansk, which abuts Ukraine's Chernihiv and Sumy provinces. Authorities there claimed that unexplained explosions also derailed two freight trains and that an armed group penetrated the region from Ukraine in March and killed two civilians.

The reported crashes raise concerns about Ukraine's capability to hit Russia and about Russia's military competence.

A spokesman for Ukraine's air force, Yuriy Ihnat, denied Sunday that Ukraine was involved in downing the aircraft. In remarks on Ukrainian television, he suggested that Russia itself could be responsible, but he later walked back the remark, saying it was an attempt at joking.

However, Wagner head Yevgeny Prigozhin offered a similar hypothesis.

"Four planes, -- if you draw a circle in the places of their fall, it turns out that this circle has a diameter (and all of them lie exactly in a circle) of 40 kilometres (25 miles). ... Now go on the Internet and see what kind of air defense weapon could be in the center of this circle, and then build your own versions," Prigozhin said on Telegram.

Prigozhin, whose forces are in the thick of a grinding monthslong battle for the city of Bakhmut, clarified that he was not "in the know" about the situation. But he has repeatedly criticized the Russian military for its strategy in Ukraine and for allegedly failing to supply Wagner with the ammunition it needs in Bakhmut.