WASHINGTON: The use of roadside bombs in Afghanistan against foreign troops and civilians has reached record highs, with US forces struggling to cut off the flow of Pakistani fertilizer used to build them.

Taliban insurgents battling US and Nato-led forces for nearly a decade are now using a growing number of improvised explosive devices (IEDs) to strike personnel or vehicles along Afghanistan's dusty roads.

The Pentagon's Joint IED Defeat Organization (JIEDDO), a specialized body tasked with putting a stop to the use of the often remote-controlled roadside bombs, offered a bleak assessment of the situation now facing foreign forces.

“During the last 12 months, an unending supply of calcium ammonium nitrate, originating almost exclusively from Pakistan, has been used to produce IEDs in Afghanistan despite a countrywide ban” on importing the fertilizer, JIEDDO spokeswoman Irene Smith told AFP.

From April to June, 3,485 IEDs exploded or were found in the war-ravaged country, according to JIEDDO - a 14 per cent increase over the same period last year. In June, use of roadside bombs was 25 per cent higher than average.

The volatile southern province of Helmand, where the Taliban are entrenched, is the worst affected, along with Kandahar province and the country's east along the border with Pakistan.

Ground troops, who are trying to reach out to the population as part of the strategy to defeat the Taliban, are particularly vulnerable to IED attacks. Use of roadside bombs against them surged 59 percent in the spring.

But coalition forces are not standing idly by. Nearly 1,900 weapons caches were discovered in the spring, three times more than in 2010, according to JIEDDO figures.

Nato-led troops have also seized 110 tons of homemade explosives and “removed over 300 high-value individuals” since the start of November, Major General James Terry, commander of ISAF forces in the south, told reporters.

In 2010, IEDs - the weapon of choice for lightly armed insurgents battling advanced militaries - were responsible for 60 percent of coalition deaths, even if only one in 10 bombs leads to casualties.

As of August 1, 738 US soldiers had been killed and 7,857 wounded by IEDs since the start of the war in Afghanistan to oust the Taliban in the wake of the September 11, 2001 attacks, according to Pentagon data.

Two more soldiers, aged 19 and 21, were killed Wednesday when their vehicle drove over a roadside bomb in Wardak province, southwest of the capital Kabul - also the scene of the deadly Chinook incident late Friday.

The IEDs have not only been used against heavily-armed foreign troops, but also against the local population, accounting for a third of all civilian deaths in Afghanistan in the first six months of 2011.

“Civilian deaths from IEDs increased 17 per cent from the same period in 2010, making IEDs the single largest killer of civilians in the first half of 2011,” the United Nations said in a mid-year report on the conflict.

On July 29, 18 Afghans were killed when a roadside bomb destroyed their minivan in Helmand province.

Most of the roadside bombs are set to explode when a person or vehicle presses down on them.

“Most of the pressure plate IEDs used in Afghanistan contain approximately 20 kilos of explosive, more than twice that of a standard anti-tank mine - yet have the trigger weight of an anti-personnel mine,” the United Nations said.

JIEDDO says an overwhelming 84 per cent of IEDs used in Afghanistan are made from calcium ammonium nitrate, developed by fertilizer manufacturers as an alternative to pure ammonium nitrate that could not be detonated.

Smith explained that the substance is “reprocessed by insurgents and then used as a homemade explosive main charge.”

Better cooperation with Pakistan, whose relations with the United States have been tense, is seen as essential to ending the flow of fertilizer into Afghanistan.

“Unless we neutralize this network, through a whole-of-government approach, we will never defeat the IED threat confronting our troops in Afghanistan,” Smith said.