A car filled with explosives blew up Thursday in the North Caucasus region of Russia, killing its two occupants, Agence France-Presse reports. A preliminary investigation suggests that the car's explosives accidentally detonated. The blast is the third to rattle Russia this week and came as Moscow was beginning to bury the 39 victims of Monday's subway attacks. On Wednesday, a separate double-suicide attack killed 12 in the North Caucasus. Doku Umarov, the leader of the Islamist group the "Emirate of the Caucasus" claimed responsibility for Monday's attacks, justifying them as retribution for "the continued assassinations of civilians in the Caucasus."