The spokesman for the Pakistani Taliban, Ahsanullah Ahsan, claimed the ban hasn't affected the group.
Dealers said they still managed to smuggle a few 50-kilogram (110-pound) bags into North Waziristan at a time and sell them for very high rates. They spoke on condition of anonymity for fear of being targeted by authorities.
A bag of calcium ammonium nitrate fertilizer, used by militants in both Pakistan and Afghanistan, can help produce two to four bombs, depending on whether they are targeting vehicles or foot patrols, according to the U.S. military's Joint IED Defeat Organization.
Insurgents either grind or boil the fertilizer to separate the calcium from the nitrate, which is mixed with fuel oil, packed into a jug or box and then detonated. Urea is dissolved in water and then combined with nitric acid to make explosives needed for a bomb.
The U.S. has struggled with the challenge of stopping militants in Afghanistan from using fertilizer to make bombs. The problem starts in Pakistan since about 80 percent of the bombs used against U.S. troops in Afghanistan are made with fertilizer smuggled across the border, according to the Pentagon.
U.S. forces used to have trouble determining which types of fertilizer to seize in Afghanistan and risked needlessly angering farmers by confiscating more benign varieties. But the military said it has introduced kits in the past couple of years that allow service personnel to test whether fertilizer contains certain chemicals, including urea and nitrate.
Militants in Afghanistan mainly use fertilizers that contain ammonium nitrate, which are banned in that country but still legal in Pakistan and often smuggled across the border. The U.S. has pushed Pakistan to regulate the sale of these fertilizers and has encouraged companies that produce them to use dye so that customs officials can more easily spot them at the border.
Pakistani authorities knew that limiting the flow of fertilizer to the tribal region would be hard on farmers but went ahead with the policy because the threat from bombings was so great, said the government official who worked on the ban.
Pakistan's neglect of the poor and underdeveloped tribal region over decades is one of the reasons the Taliban insurgency that flared up there has been so difficult to extinguish. The Pakistani military has conducted a series of offensives in all parts of the tribal region except for North Waziristan.
The army plans to step up operations against the Taliban and their allies in North Waziristan in the near future, according to Pakistani and U.S. officials.
If that happens, the army may not want to count on the support of local farmers.
"This fertilizer ban is destroying us," said Ilyas Khan, a farmer from Mir Ali. "All we can do is pray for the situation to improve so we can resume our normal business."
Abbot reported from Islamabad. Associated Press writers Zarar Khan in Islamabad and Riaz Khan in Peshawar, Pakistan, contributed to this report.
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