Mohibullah Mohib, a spokesman for the provincial police chief, told RFE/RL that the incident occurred while the bus was traveling on the Kandahar-Herat highway in the Ab Khorma area on the morning of July 31.

No militant group immediately claimed responsibility for the blast, but Mohib accused the Taliban of planting the bomb to target Afghan and foreign security forces.

Taliban spokesman Zabihullah Mujahi denied that, saying the militant group was not responsible for planting land mines in the area.

Mohib said that most of the dead or wounded were women and children, and that ambulances had taken victims to hospitals in Farah and Herat provinces.

In a report published on July 30 , the UN Assistance Mission in Afghanistan (UNAMA) said that civilians were being killed and wounded at a "shocking" level in Afghanistan's conflict.

Casualties have dropped 27 percent in the first half of 2019 compared to the same period last year, which was a record.

Nonetheless 1,366 civilians were killed and another 2,446 injured during the period, UNAMA said.

The bloodshed comes amid a months-long, U.S.-led push to forge a deal with the Taliban to end the nearly 18-year war in Afghanistan as the country gears up for a presidential election set for September 28.

The militant group controls or contests around half of Afghanistan, more territory than at any time since the U.S.-led invasion in 2001 ousted the group from power.

With reporting by AP and AFP