Kandahar provincial police Chief Matiullah Khan Qaneh said the militants seized control of a bus Thursday, taking nearly 50 passengers hostage, CNN reported.
The militants later released 10 of the kidnapping victims, but then executed the remaining hostages Thursday, Qaneh said.
"According to our information from the area, Taliban killed the remaining 40 passengers," the provincial official said.
But contradictory reports have come in from Afghan Gen. Zahir Azimi and a Taliban spokesman, CNN reported.
Azimi cited the number of civilian casualties at 31, while Taliban spokesman Qari Mohammad Yousif Ahmadi claimed the only victims were 27 Afghan soldiers.
"They were all army soldiers from Laghman province and they were going to Helmand province to support the governor," Ahmadi told CNN.