KANDAHAR, Afghanistan — Taliban militants stopped a bus traveling on Afghanistan's main highway through a dangerous part of the country's south, seized about 50 people on board and killed around 30 of them, officials said Sunday.

A Taliban spokesman took responsibility for the attack but claimed to have killed 27 Afghan army soldiers. Afghan officials said no soldiers were aboard and all the victims were civilians.

Militants stopped the bus traveling in a two-bus convoy in a Taliban-controlled area about 40 miles west of Kandahar, said provincial police chief Matiullah Khan.

He said two buses had been traveling together, and the militants had tried to stop the first one but failed. He said the insurgents fired at the first bus, killing a child on board.

Officials offered varying death tolls from the attack, which occurred in an area where government forces cannot travel safely without heavy military protection. That may explain why news of Thursday's killings did not emerge until Sunday.

The Afghan Defense Ministry spokesman, Gen. Mohammad Zahir Azimi, said 31 people were killed and that six of the dead were beheaded in a separate area from where the other 25 bodies were found.

Khan originally claimed about 40 civilians were killed but later Sunday, he lowered the death toll telling a news conference 24 people had been killed. He said the victims had come from northern Afghanistan and were between 20 and 25 years old.

Khan said authorities had arrested four Taliban commanders in connection with the attack.

There was no way to independently verify the number of victims.

"The Taliban want to hide the news that they arrested and killed innocent Afghan civilians," Khan said, dismissing their claim the victims were soldiers.

Taliban spokesman Qari Yousef Ahmadi said militants looked at the documents of those traveling on the bus, released all the civilians and killed only soldiers.

Taliban attacks have become increasingly lethal this year, as the militia has gained power and surged throughout southern and eastern Afghanistan. Violence in Afghanistan this year has killed more than 5,100 people — mostly militants — according to an Associated Press count of figures from Afghan and Western officials.