For four years, American forces in Afghanistan have been throwing technology at the deadliest military challenge of this generation.
As the Taliban buried more and more improvised explosive devices (IEDS), which kill more U.S. troops than any other weapon, the military built multi-million dollar trucks that deflect the impact of an explosion. The Taliban built bigger, more effective bombs. The military built sophisticated equipment to jam cell phones that triggered the bombs. The Taliban started using detonation cords or pressure plates instead of wireless signals.
Now, the U.S. has decided to go to the source of the problem, and that has led the U.S. out of Afghanistan -- to Pakistan.
"We're not going to solve the IED problem inside Afghanistan," says a senior U.S. military official who spoke on condition of anonymity. "If we don't go after the supply, we're playing defense."
The supplier is not a bombmaker, but one of the largest companies in Pakistan. Pakarab is the nation's major producer of the fertilizer calcium ammonium nitrate -- the raw ingredient for as many as 75 percent of the IEDs in Afghanistan, according to a U.S. military official. The fertilizer is completely legal in Pakistan, where a quarter of the GDP, and half of the workforce, depends on agriculture. But CAN, as the fertilizer is commonly known, is illegal in Afghanistan, and enough of it is crossing the porous border between the two countries to help create some 16,000 bombs this year, a 200 percent increase since 2008.
"We are capturing hundreds of thousands of pounds of CAN, much of it in original bags, with detonation cord, with plastic caps, with time fuses from Pakistan," says a senior U.S. military intelligence official. "You get a complete system, including CAN, to make hundreds if not thousands of IEDs… There's no doubt it's all coming from Pakistan."
But this is not just another blame-Pakistan story. In interviews with a dozen U.S. military, diplomatic, and political officials who work on stopping IEDs, not a single one blamed the flow of CAN into Afghanistan on Pakistan's military or its powerful intelligence service, though both are often accused of sheltering the insurgents who attack U.S. troops in Afghanistan.
In fact, the U.S. military officials praised Pakarab for cooperating. The officials acknowledged the use of legal fertilizer to make illegal bombs was a new concept for the Pakistanis, but said Pakistan's government must help, and they portrayed IEDs as a problem that the U.S. and Pakistan could confront together, and perhaps use to improve the strained relationship between the two countries.
The officials had agreed to speak only on the condition of anonymity because of the delicacy of the U.S.-Pakistan relationship, tested most recently when NATO helicopters killed 24 Pakistani soldiers in November.
IEDs are one of the few areas where the two countries' interests truly align: Pakistani military officials say IEDs have killed more than 1,000 Pakistani soldiers, and 2,000 Pakistanis total, since August 2010.
"The main weapon of the terrorists in [the tribal areas] is IEDs," said a senior Pakistani military official.
The U.S. also acknowledges that only about 1 percent of Pakarab's CAN is falling into the wrong hands. The U.S. has no intention of shutting down the company, which made more than $100 million in profit last year, but U.S. officials are desperate to find out how the fertilizer goes from legally produced to illegally smuggled, and in so doing find a way to stem the huge increase of IEDs in Afghanistan.
In late December, President Obama signed into a law a bill that requires the Pentagon to certify that Pakistan is trying to reduce the flow of IED materials before it can send hundreds of millions of dollars in aid to Pakistan.
"A commitment has been made to us and to others in our government that they were going to implement their counter-IED strategy," Sen. Bob Casey, D-Pennsylvania, told ABC News in a phone interview. Sen. Casey recently visited Pakistan to speak to the government and military about IEDs. "That just hasn't happened, at least not to the extent that we wanted."
Pakarab's factories are hundreds of miles from the Afghan border, in the southern Punjabi city of Multan. The area is notorious for local militant groups with global aspirations, but Pakarab is a model of profit and efficiency. A household name for any farmer in Pakistan, the company is successful and widely respected, and trying to become the first Pakistani company to be listed on the New York Stock Exchange.
Pakarab produced 350,000 metric tons of calcium ammonium nitrate last year. But that's pretty much where everyone's knowledge ends. The company has not been required to track where the fertilizer goes after it's sold.
"That's where it gets difficult," said a U.S. official in Pakistan. "As of now, there's no regulation after that point."
Pakistan's interior ministry -- which declined multiple requests from ABC News for an interview -- has created a counter-IED strategy designed to identify buyers and track the movement of CAN. But the plan is a huge undertaking in a country where rule of law infrastructure is weak: despite suffering from some of the worst terrorism in the world for the last 10 years, Pakistan's courts have not convicted a single terrorist since 9/11.
The interior ministry and the U.S. embassy in Pakistan are working together to create better laws and train police and prosecutors to try and convict militants who create IEDs; better track where the fertilizer goes by registering sellers and tagging bags with the same "No Objection Certificates" that diplomats are required to carry; and, at the last stage, strengthen the checks made on the roads leading into Afghanistan. Pakistani officials have even spoken of creating "restriction zones" where CAN would be banned a certain distance from the Afghan border.
But the U.S. official in Pakistan said those efforts are in "very draft form."
In the U.S., "we take it for granted that there's a working police force, that the courts work… and if you make it a priority and stay focused, you can eradicate," says Casey. "I wonder sometimes even with a full commitment, how able would they be to execute their plan, given their institutions?"
It's also not clear how quickly the plan to step up regulation of CAN is being implemented. Pakarab said in a statement provided to ABC News it had not yet been told by authorities to track sales of the fertilizer.
"The Government of Pakistan has not mandated that the fertilizer be tracked after it leaves the factory," a company spokesman said in the e-mailed statement.
But the company said it has been working with both "the Pakistani and U.S. governments to make the product safer and identifiable. As an initiative from the company's side the packaging for CAN fertilizer has already been made distinguishable for easy detection."
Pakarab has also tentatively agreed, according to a separate U.S. official, to dye CAN a shade of yellow so it can be easier detected at the border and identified if found in a bomb in Afghanistan. Pakarab said it has been testing a dye, but would not confirm it had made any decisions. Initial tests "are encouraging and lab testing and in house development of more samples is underway," the company spokesman said. "This is likely to assist in quick detection and traceability."
It is not clear how Pakarab's 2,500 retailers, or Pakistan's large agricultural landowners -- some of the country's most powerful people -- will react to strange-looking fertilizer once it is sold widely in Pakistan.
The U.S. military has had some recent success intercepting CAN crossing the border from Pakistan into Afghanistan.
This summer, U.S. troops discovered 5,000 pounds of Pakarab calcium ammonium nitrate hidden beneath a floorboard of a truck, still in original bags. But they admit they still don't know enough about the networks that move the fertilizer or just how large they are.
"It's like narcotics crossing the U.S. border," said the senior U.S. military intelligence official. "We don't know if we're getting 1 percent or 10 percent that's crossing." The U.S. has also had some success targeting bombmakers.
Two senior military officials cited the case of a raid in Afghanistan's Paktika province that killed 11 militants. IEDs did not return to the immediate area, the officials said, for seven months.
When pressed, however, U.S. officials concede that the porous border, weak Pakistani law enforcement and the relatively small amount of CAN required to make bombs mean the flow of bomb ingredients might never be completely stopped.
"There is no silver bullet to fix this problem," said the U.S. official in Pakistan, a phrase repeated almost exactly by three of the U.S. officials interviewed for this story.
Military advocates of counterinsurgency believe that ultimately, the problem might have to be tackled inside Afghanistan, by using Afghans themselves as the bomb detectors.
In Kandahar, for example, U.S. military officials say that after a surge of U.S. troops removed insurgents from traditional safe havens, the number of weapons and materiel caches reported to them by the local population spiked by 400 percent.
"The tipping point is preventing attacks and giving confidence to the population," a senior U.S. military official said. "They become your defense."
But the U.S. government has clearly decided to try and make pressuring Pakistan to limit the CAN crossing the border one of its top priorities -- even if all that is possible in the end is to make CAN-based IEDs more expensive and difficult to make.
"CAN has a legitimate use and banning isn't a realistic strategy in Pakistan, where agriculture is so important," says Casey. "But if we can just make it a little harder for the guy building the bomb, it's worth our time."