A roadside bomb struck a passenger bus in western Afghanistan on Tuesday, killing at least 11 people, including women and children, officials said.

The morning attack in the Bala Buluk district in western Farah province also wounded 31 people, all civilians, according to Abdul Jabar Shahiq, the provincial health department chief.

Shahiq said the bus was on its way from Herat province toward the capital, Kabul, when it hit the roadside bomb.

No group immediately claimed responsibility for the bombing but the Taliban have a strong presence in the province, especially in Bala Buluk where they often plant roadside bombs to target government officials or Afghan security forces.

Such attacks often end up inflicting significant casualties among civilians.

The latest report by the United Nations says the number of civilians killed in Afghanistan in the first half of this year increased by 1 percent, compared to the same period last year. The U.N. mission in Afghanistan said the number — 1,692 killed by violence — is the highest 6-month death toll since the systematic documentation of civilian casualties started in 2009.

Since the United States and NATO formally concluded their combat mission at the end of 2014, a resurgent Taliban have stepped up attacks across the country and an Islamic State affiliate has also emerged, staging high-profile attacks that have claimed scores of civilian lives.

Farah province has seen heavy fighting in recent months, with local officials and tribal elders requesting additional government forces to support the overburdened army and police.

In May, more than 300 Taliban launched a multi-pronged attack on the city of Farah, the provincial capital, before they were repelled. At least 25 government troops were killed in the fighting.

Meanwhile, the Islamic State group on Tuesday claimed responsibility for an attack the previous day in eastern Nangarhar province that killed a tribal leader and three others. In Monday's attack, a suicide car bomber targeted and killed Haji Hayat Khan, the commander of a local militia battling both the Taliban and IS militants.

In a statement posted by the IS affiliate's Aamaq news agency, the militants warned all those fighting against them would meet the same fate.

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Associated Press writer Maamoun Youssef in Cairo contributed to this report.