( CNN ) -- Six members of mine-removal team were killed and three others were abducted following an ambush by gunmen in western Afghanistan on Thursday , a police official said . The attack took place as the team was traveling to work in the Kohsan district of Herat province . All of them worked for the HALO Trust , a UK-based mine clearance agency , according to Abdul Rauf Ahmadi , a spokesman for Herat 's police chief . The organization has 150 mine defusing teams and employs more than 3,000 Afghans , it says on its website . It also destroys other munitions . Since the Soviet Union invaded Afghanistan in 1979 , multiple warring parties have laid landmines , bringing the total number of mines to as many as 640,000 , Halo Trust reports . Afghanistan is one of the most-mined countries in the world , according to HALO . In January , armed men abducted 68 members of another landmine-removal team . 4 service members among 16 killed in eastern Afghanistan attack .
The landmine crew was on its way to clear areas of Herat province . A spokesman for the Afghan army said that a roadside bomb had exploded in an area where soldiers were clearing land mines.