Farmers have struggled with other crops

A number of other people, including three other soldiers, were injured in the clash, which authorities said lasted several hours.

Pakistan is trying to clamp down on the farming of poppies - the raw material used to make opium and heroin - after a resurgence in the crop in the past several years.

The country had been declared poppy-free by the United Nations. But in February, the UN's drugs monitoring body said it was concerned about a resurgence in poppy cultivation in Pakistan and neighbouring Afghanistan.

Authorities in the northern province of Balochistan last week began a massive operation to destroy poppy fields.

About 1,000 officials are taking part in the operation in the Gulistan and Inayatullah Karaiz areas, 100 kilometres (60 miles) north of Quetta, near the Afghan border.

Many farmers have held protests, saying opium cultivation is their only means of making a living.

The director of Pakistan's anti-narcotic force, Liaqat Ali Toor, told the Daily Times newspaper detailed meetings had been held with local people to win their permission to destroy the poppy fields.

He said the crop had been cultivated for the first time in Balochistan last year and that officials had only discovered it this year.

Mr Toor said all efforts would be made to eradicate poppies throughout Balochistan, where the crop has been farmed in about 1,500 acres.

Angry farmers say a long drought in the area and soaring taxes have hit them hard.

Others support the steps taken by the government, but say the farmers must be given help with alternative sources of income.