The Russian military says one of its fighter jets has crashed in Syria, killing two pilots on board.

The Su-30SM jet was not shot down and may have crashed because of a bird in the sky, Russian media cited the military as saying on Thursday.

“As it was climbing after taking off from the Hmeimim airbase, the Russian fighter Su-30SM crashed into the Mediterranean Sea. Two pilots, who fought until the last minute to save the plane, died, according to reports from the scene,” the Russian Defense Ministry said in a statement.

Hmeimim is a western Syrian airbase currently operated by Russia.

It further said, “According to preliminary information, the reason for the crash could have been a bird falling into the engine.”

Moscow also runs a naval facility in the Syrian city of Tartus, which is similarly situated in the Arab country’s west.

The accident brings Russia’s official military losses in Syria to 86, AFP reported.

Moscow and Damascus have been cooperating since late 2015 towards containing Takfiri terrorism and foreign-backed militancy.