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.