A suicide car bomber has attacked Afghan police providing security to US forces in eastern Afghanistan, killing at least 18 people, government officials said.

The attack, responsibility for which has been claimed by the Taliban, took place around 8:30am (04:00 GMT) on Saturday near a stadium and bus station in Khost City, Mubariz Zadran, a spokesman for the governor of Khost province, told Al Jazeera.

"Eighteen people were killed and 10 people injured, including two children," Zadran said. "The target of the attack was Afghan police and US forces, but most of the victims were civilians."

Saturday was a public holiday in Afghanistan as it marked the first day of the Muslim holy month of Ramadan.

In clear defiance to a call by the United Nations Assistance Mission in Afghanistan for a ceasefire during Ramadan, the Taliban announced on Friday they would intensify their attacks during the month.

Separately, 10 civilians, including women and children, were killed and six others were wounded when a minibus hit a roadside bomb in Afghanistan's western Herat province on Friday.

The incident took place in Adraskan district of Herat on Friday morning, Abdul Ahad Walizada, a spokesman for the Herat provincial police, said on Saturday.