Herat - Afghan authorities on Wednesday recovered the bullet-riddled bodies of seven passengers kidnapped by gunmen in the western province of Farah a day earlier, in an attack blamed on Taliban insurgents, police said.

The violence, which underscores the fragile security situation in Afghanistan, came after Taliban fighters closed a highway connecting provincial capital Farah to Herat city late Tuesday, stopping a bus and forcing 16 passengers to dismount, Farah police spokesman Iqbal Baher told AFP. They shot at least seven of them, while the remaining nine were taken hostage, he said.

Government forces launched an operation early Wednesday to free the hostages and open the highway, clearing roadblocks set up by the militants, Baher said. They recovered the bodies of seven passengers, he continued, adding that six were civilians and one a police officer.

"It is not clear why the Taliban kidnapped and killed them, and we are still unsure about the fate of the remaining kidnapped passengers," he stated.

The Taliban have so far not commented on the incident in Farah province, which has witnessed an increase in the militant group's activities recently, according to provincial officials. Highways around Afghanistan passing through insurgency-prone areas have become exceedingly dangerous, with the Taliban and other armed groups frequently kidnapping or killing travellers.

Civilians are increasingly caught in the crosshairs of Afghanistan's worsening conflict as the Taliban step up their annual spring offensive, launched in April against the Western-backed Kabul government.

Six civilians seeking work in Farah, capital of western Farah province, were killed earlier this month when their pickup truck hit a roadside bomb. Authorities blamed the Taliban for the attack.