Dozens of civilian passengers, mainly women and children, have been killed in Afghanistan when the bus they were travelling in ran over a roadside bomb, officials have said.

“A passenger bus travelling on the Kandahar-Herat highway hit a Taliban roadside bomb. So far at least 28 killed, 10 wounded,” said Muhibullah Muhib, a spokesman for western Farah province, of the incident on Wednesday morning. All were civilians, mostly women and children, he said.

Farooq Barakzai, a spokesman for Farah’s governor, confirmed the toll but warned it might rise.

There was no immediate confirmation from the Taliban that it was behind the attack.

It came a day after the United Nations said civilians were being killed and wounded at a “shocking” level in Afghanistan’s war, despite a push to end the nearly 18-year-old conflict.

Casualties have dropped 27% in the first half of 2019 compared with the same period last year, which was a record, but nonetheless 1,366 civilians were killed and another 2,446 injured. The UN branded efforts to reduce the violence “insufficient”.

It also said that US and pro-government forces caused more civilian deaths than the Taliban and other insurgent groups for the second quarter running.

Child casualties represented almost a third of the overall total of civilian casualties.

The bloodshed comes amid a months-long, US-led push to forge a peace deal with the Taliban that would see foreign forces quit the country in return for various security guarantees.