Washington: Pakistan is a major source of makeshift bombs being used by terrorists in Afghanistan, a media report said.

More than 80 percent of the improvised explosive devices (IEDs) are homemade explosives using calcium ammonium nitrate fertilizer produced in Pakistan, according to Navy Captain Douglas Borrebach, Deputy Director (Resources and Requirements) at Pentagon's Joint IED Defeat Organization, a daily reported.

"The border is a sieve. You can do your checkpoints, but that's not going to help stem the supply," Borrebach said.

Top American Senator Robert Casey, who travelled to Pakistan in Afghanistan, has met top Pentagon officials in this regard, urging them to press Pakistan take action against such IEDs.

"From June through August, US troops detected or were hit by 5,088 improvised explosive devices (IEDs), the most for any three-month period since the war began in 2001," the report said.

Choking off the source of fertilizer is critical, Borrebach said.

"How do we work with Pakistan to be able to reduce the amount of calcium ammonium nitrate coming across the border? That's the key to this," Borrebach said.