Vladikavkaz, Russia ? A female suicide attacker detonated a bomb Thursday near a bus carrying soldiers and civilians to work at a military airfield near Chechnya, killing at least 16 people. It was the third suicide attack in the Russian Caucasus in less than a month.

No one claimed responsibility, but suspicion fell on Chechen rebels who have been fighting Russian forces for more than 3 1/2 years. Russian soldiers are reported killed in rebel attacks in and around Chechnya almost daily.

The red-and-white bus was headed from the city of Mozdok in the North Ossetia region, the military headquarters for Russian operations in Chechnya, to a nearby airfield when the woman approached as it stopped near a railway crossing and blew herself up, officials said.

There were conflicting reports about whether the woman — dressed in a white coat, the customary uniform of medical personnel — got on the bus or detonated her explosives from outside.

The force of the blast blew out some of the bus’ windows, cracked others and left the side of the vehicle pockmarked with holes and dents. Citing regional prosecutor Alexander Begulov, Channel One television said the bomb was filled with metal balls.

Russian prosecutors said the death toll was at least 16, though it wasn’t clear if that figure included the attacker.

The passengers included an air crew and support workers from the Prokhladny air base four miles from Mozdok.

The attack dealt a further blow to the Kremlin’s efforts to portray Chechnya as increasingly stable after a decade that has seen two wars and widespread lawlessness.