The explosion happened as the bus travelled through Bala Baluk district
At least eight killed in roadside bomb in Afghanistan
At least eight people were killed when a roadside bomb hit a Kabul-bound passenger bus in western Afghanistan on Tuesday, officials said.
"It was a bomb planted by the Taliban to hit security forces but unfortunately it got a passenger bus," Muhibullah Muhib Farah, provincial police spokesman, told AFP.
About 40 people, mostly women and children, were injured.
Provincial governor spokesman Naser Mehri said the blast took place as the bus travelled through Bala Baluk district of Farah at 4.30am local time (4am UAE time).
Photos posted on social media showed the vehicle's blackened shell and dozens of Afghan men at the scene.
There was no immediate confirmation the Taliban were behind the explosion.
Around a dozen of the wounded — mostly members of the Hazara ethnic group — were taken to hospital in Herat.
Among them was Mohammad Zahir, 40, who had been travelling with his newly married daughter to visit relatives in Kabul.
"The bus was driving on the main road when I heard a big bang," Mr Zahir told AFP.
"When I woke up I found myself in the hospital. I still don't know what's happened to my daughter."
Afghan President Ashraf Ghani condemned the attack.
"Harming civilians, especially scholars, children and women, is against the Ulema Council's (Afghanistan's top religious leaders) fatwa," Ghani said in a statement, referring to the group's proclamation in June that suicide attacks and explosions were "haram" or prohibited in Islam.
Civilians have borne the brunt of the 17-year conflict and improvised explosive devices, such as remotely detonated or pressure-plate bombs, are one of the main cause of casualties.
Such IEDs caused 877 civilian casualties in the first half of 2018 — 232 deaths and 645 wounded — accounting for 17 per cent of overall civilian casualties, the latest UN figures show.
A total of 1,692 civilians were killed in the conflict during the first six months of this year. Another 3,430 were wounded.
That was the highest number of civilian fatalities for the period since the United Nations Assistance Mission in Afghanistan began keeping records in 2009.
Militant attacks and suicide bombs were the leading causes of death.
The Taliban has a strong presence across western Afghanistan, particularly in Farah. It launched a major attempt to take over the provincial capital in May, triggering intense fighting with US and Afghan forces.
After a day-long battle the Taliban fighters were forced to the outskirts of the city.