Tatarstan investigators opened a criminal case Monday after discovering an exploded car that they believe was carrying militants.
Investigators said in a statement on their website that a VAZ-2110, better known under its nickname "Zhiguli," was discovered Sunday night near the Kazan-Zelenodolsk highway.
After studying the surrounding area, "the remains of what looked like three people, a Kalashnikov assault rifle and religious literature were found," the statement read.
Investigators believe that the accidental explosion was triggered when the alleged militants were arming a bomb.
A criminal case has been opened on charges of organizing a terrorist attack and illegal weapons trafficking. Investigators said they were conducting further searches at the scene of the explosion.
Last month, two of Tatarstan's moderate Muslim clerics were attacked in the region's capital, Kazan. One of them, Valiulla Yakupov, who headed the Spiritual Board of Muslims' education department, died shortly after being shot by unidentified gunmen.
The other, chief Mufti Ildus Faizov, received multiple injuries, including two broken legs, after assailants detonated three car bombs in his SUV.
Islamist militant Rais Mingaleyev has claimed responsibility for the attacks.