WASHINGTON The world's most powerful military machine is scrambling to fight a simple, low-tech weapon in Afghanistan that is killing and maiming American and allied soldiers at an alarming rate.

The homemade bomb - often a mixture of fertiliser, fuel and metal - is the number one killer of Nato troops in Afghanistan and the US military has launched a massive, costly effort to try to defeat it.

In Iraq, the Americans eventually managed to contain the scourge partly by employing jamming devices and large numbers of unmanned aircraft that could watch for people planting roadside bombs.

But the rudimentary improvised explosive devices (IEDs) in Afghanistan have no radio frequency to jam while the country's vast, rural landscape makes surveillance a daunting task, according to US officials.

“You've got an entirely different challenge in Afghanistan,” said Gen Thomas Metz, head of the Pentagon's Joint Improvised Explosive Device Defeat Organisation (JIEDDO).

“It looks about like the moon sometimes. It's huge, open spaces. Not much vegetation. It's an unbelievable, tough, rugged terrain,” he told reporters after a congressional hearing.

American soldiers learned to identify suspicious objects on paved streets in Iraq, but Nato forces in Afghanistan have trouble picking out trip wire or booby traps on dirt roads, said Command Master Sergeant Todd Burnett of JIEDDO, who regularly visits troops on the Afghan front.

Soldiers who only recently arrived in Afghanistan are still trying to figure out how to handle the IED threat there, he said.

“For so long we've been focussed on Iraq,” he said. “We're still learning the environment over there... We're playing catch-up.”

And unlike Iraq, where much of the resistance was concentrated in city centres, in Afghanistan the bombs are spread over an enormous area, he said.

The threat has steadily mounted in Afghanistan, with more than 1,000 IEDs found or exploded in August - a dramatic increase from just a year ago.

But the scale of the threat is still much lower than what US and Baghdad forces faced at the height of resistance in Iraq, when the number of IED incidents rose to about 2,500 a month.

Gen Metz, charged with leading the effort against the homemade bombs, said eliminating IEDs is unrealistic, but he talks about the need to get “left of the boom” - by detecting the bomb before it goes off and targeting the bomb-making networks.

His organisation, set up initially in 2006 to tackle the scourge in Iraq, invested close to a billion dollars over the past year in technology, training and other initiatives to battle the homemade bombs.

Metz said he hopes sensors and software can be refined soon to detect small changes on the ground, revealing where a militant may have dug up a road or set down a trip wire.

But he said the “game-changing” technology is still not there.

“We're left with some real tough physics problems,” he said, as the sensor has to deliver reliable information soon enough to allow a vehicle speeding down the road to stop before reaching the bomb.

To protect troops, the Pentagon is rushing the production of new armoured vehicles for Afghanistan as a version designed for Iraq has proved too bulky for the country's treacherous terrain.

Seven of the new MATVs have been delivered and the Pentagon has approved plans to quickly produce more to ship to Afghanistan.

While President Barack Obama weighs a request for a major troop build-up, Defence Secretary Robert Gates already has deployed nearly 3,000 soldiers who are trained in explosive disposal, intelligence and route clearance to contain the IED threat.

Commanders are working to shift much of the coveted unmanned aircraft fleet from Iraq to Afghanistan to spy on people planting bombs, and the military has bought new, smaller robots that can help soldiers dismantle explosives in a more rugged setting.

In the meantime, the IEDs are wreaking havoc, killing and badly wounding Western troops and Afghans while piling pressure on the Nato-led mission.

With the carnage from the bombs undermining public support for the war on both sides of the Atlantic, some lawmakers in Congress say the military has to move faster.

The Pentagon has promised anti-IED programmes will produce results “soon” but the death toll keeps rising, said Representative Duncan Hunter at a congressional hearing on Thursday.

“We've been... told that since I got into office in January. 'It's going to be there soon, sir. It's going to be there soon,'” said Hunter, a Marine veteran who served in Iraq.

“It isn't there now. And we're losing guys every day. So what are we going to do tomorrow to defeat IEDs so that we don't have any more IED deaths?”—AFP