At least 29 Taliban fighters were killed in southern Afghanistan when they tried to attack a government-backed poppy eradication mission in the area, police said.

According to General Mohammad Hussein Andiwal, police chief of Helmand province, the clashes had gone on for six hours on Wednesday in the Marja district, leaving 25 fighters dead.

Four fighters were killed on Thursday when a landmine they were planting in a road in Helmand province exploded early, Andiwal said.

The mine had been intended for the team involved in poppy eradication working in the Marja district.

"Police went to support the eradication. The six-hour fighting killed 25 Taliban and two Taliban were arrested," he said.

Yousuf Ahmadi, a Taliban spokesman, confirmed the fighting but said only one fighter was killed.

Helmand is the centre of Afghanistan's drugs industry, which produces more than 90 per cent of the world's opium, the main ingredient of heroin.