Unknown gunmen have abducted more than 60 Afghan workers clearing Soviet-era anti-tank mines in western Herat province, the largest mass kidnapping of its kind in the province.

Herat, which borders Iran, has long been plagued by kidnappings, but a sharp downturn in security in the traditionally safe province would be a worrying sign ahead of the departure of most foreign forces by the end of this year.

More than 60 Afghans working for the British mine-clearing group, the Halo Trust, had arrived at a village in Pashtun Zarghun district before 8am local time to begin clearing anti-tank mines left over from the 10-year Soviet occupation of the 1980s.

Halo Trust programme manager's in Afghanistan, Farid Homayoun, told Al Jazeera that the men were stopped by gunmen on motorcycles and taken to a mountainous area and had not been seen since.

"Some de-miners were able to escape but over 60 staff are still with those people and at the moment, the local shura are in negotiation for their release," Homayoun said, using the Afghan word for council.

No demands have been made by the abductors and it is not known who is responsible but provincial police have been sent to a nearby village.

Officials in the district said six workers and four vehicles had been recovered and a search was under way for the other abducted men.