Two Russian Su-35S fighter jets collided in the air over Russia’s Kursk region.

Axar.az reports, citing The Moscow Times, that one of the pilots was killed in the collision.

Ukraine has not confirmed any involvement in the incident, while Russia’s Defense Ministry had not issued an official comment at the time of publication.

The Su-35S is a Russian multirole fighter aircraft considered one of the most advanced in Russia’s arsenal. It is equipped with the Irbis radar system and can carry long-range R-37M air-to-air missiles.

The incident comes after Ukrainian forces reported destroying a Russian MiG-29 fighter near the Millerovo airfield and a Ka-27 helicopter near the Yeysk airfield on Sept. 2.