Algeria is suffering a potato shortage because officials have imposed strict controls on the use of fertiliser to stop al Qaeda militants using it as a bomb-making ingredient, farmers said.

    Security experts say ammonia, used by farmers to improve crop yields, has also been found in bombs detonated by Algerian militants affiliated to al Qaeda.

    State security forces in this North African country have cracked down hard on the insurgents but farmers say there has been an unforeseen consequence: a kilo of potatoes in the capital now costs more than three times what it used to.

    "Lack of fertilizers, particularly ammonia, is the key reason behind the rise in the price of potatoes,"Azizou Redouane, a 28-year-old farmer from the Ain Defla region, 120 km (75 miles) west of Algiers, told Reuters.

    Algerian farmers have to apply to their local chamber of agriculture, a farmers' syndicate, for approval to obtain fertiliser.

    Farmers said even if they were given clearance to buy ammonia, in some cases they were still required to bring the chemical to their farms under police escort to make sure it did not fall into the wrong hands.