"Basically what we're waiting for is for Pakistan government to implement the strategy that they've said they're going to implement when we were in Pakistan in August, meeting with all highest-level officials," said Sen. Robert Casey, D-Pennsylvania. "Unfortunately we're into October now, and I haven't seen any action in September," CNN quoted him as saying.
He said strategy should include restricting who has access to fertilizer; tracking it, perhaps with use of dye; and interdicting it at the border with Afghanistan.
According to US military's Joint IED Defeat Organization, 84 percent of improvised explosive devices in Afghanistan are made from fertilizer produced in Pakistan.
IEDs are the number one killer of American forces in Afghanistan, responsible for more than 400 deaths in the past two years.
But a Pakistani official disputed Casey's criticism, saying authorities are moving as fast as they can on the problem, and that it has to be a joint effort on both sides of the border.
The official, who declined to be identified, also said that out of tons of fertilizer produced, it is difficult to track small amounts placed into IEDs.
"It's an extremely porous border," said Seth Jones at RAND Corp., who was in Afghanistan last month.
"There's not enough time in a day, with a long line of vehicles, to stop every single vehicle and check it."
He claimed militants in Afghanistan are managing to smuggle IED ingredients up Helmand River Valley to make roadside bombs targeting US Marines operating in southern Afghanistan, as well as through areas like Khyber Pass to target U.S. Army forces in the east.
Casey said he would not be put off, as long as American soldiers are being injured and killed. "Go to Walter Reed, and see those 19-year-old kids with half of their leg blown off -- or in many instances, having died this way," he said. "That's just inexcusable, when we have resources, technology, and know-how, to slow this down or to stop it in some way."