Afghan officials say six members of a team removing mines in Western Farah province who were kidnapped last week have been killed.
Several bodies were recovered in Farah's Bakwa district on Sunday, local police official Mohammad Munir the Reuters news agency.
Al Jazeera's Bernard Smith, reporting from Kabul, said that 31 people from the Demining Agency of Afghanistan (DAFA) were reported to have been abducted in the province on July 6.
"They were extremely brutally treated," he said. "Four of them were tied to the back of vehicles and dragged until they died."
Two of the kidnapped men from DAFA, a non-governmental organisation based in Kandahar which focuses on landmine clearence in the southern and western Afghanistan, were released on Sunday and taken to hospital.
Police officials gave conflicting reports as to whether some of the men had been beheaded.
Abdul Baseer, a Farah provincial council member, accused the Taliban of the abductions and killings.
But Taliban spokesman Qari Yousuf Ahmadi said the men had been abducted by outlaws in Farah and the Taliban were not involved.
In other developments in Afghanistan, the district governor of Moqur in western Badghis province was killed by a roadside bomb on Sunday.
Police said the explosion also wounded four of the governor's bodyguards and one civilian.
In Kandahar, two policemen and once civilian were killed and six others, including three civilians, were wounded when a homemade bomb detonated near a police vehicle.
"The explosives detonated around 0800 [on Sunday] and resulted in martyring two policemen and one civilian and injuring three policemen and three civilians," the interior ministry said in a statement.
Two International Security Assistance Force members were were also killed in seperate attacks in eastern and southern Afghanistan, NATO said in a statement.
Sunday's violence comes a day after General David Petraeus, the out-going commander of NATO forces in Afghanistan, said violence had started to decline on an annual basis for the first time in five years, defying predictions by intelligence analysts.
"Obviously, it is what we have wanted to see-rather than the year-on-year-on-year increase that has taken place for some four or five years," Petraeus said in what was expected to be his last media briefing before he steps down from his current post to take over as CIA director in September.
"It is an important development but we need to see if it is sustained or not."
Source: Al Jazeera and agencies