Explosive ordnance disposal troop commander Lt. Caroline Pollock squats by a culvert on a dusty training ground and looks at what appears to be a pile of harmless junk. A plastic jug. Some metal casing. Wiring. All the makings of deadly roadside bombs.

Such bombs, which the military calls improvised explosive devices, or IEDs, have long been the most feared insurgent weapon. Combating the threat has taken on new urgency as the surge of 37,000 new U.S. and NATO troops means more targets for the bombs.

"The IED fight is like a chess game, in which only one side plays by the rules," said Canadian Maj. Chris Cotton, commanding officer of the Task Force Kandahar counter-improvised explosive device squadron. "We are very diligent about studying each event. But that is what the bad guys are doing, too."

Cotton said IED experts are getting better at finding the explosives before they go off, but added it is a constantly evolving battle that exacts a high toll. As coalition forces add more armor on their vehicles, for example, the Taliban have increased the size of their explosives.

"Casualties to IEDs significantly outnumber casualties to any other threat," Cotton said. "They are efficient, cheap, and omnipresent. IEDs are obviously the enemy's weapon of choice right now."

Pollack said some of the improvised explosives consist of material that costs as little as $50.

There were more than 7,000 IED incidents in 2009 — including explosions, the discovery and defusing of the bombs or civilians turning them in — compared to just 81 in 2003, according to U.S. intelligence figures.

An Associated Press count, based on daily reports from NATO's International Security Assistance Force, found that 129 of the U.S. fatalities in 2009 — or more than 40 percent — were caused by IEDs. About three-quarters of all American deaths and injuries in Afghanistan are believed to have been a result of improvised explosives.

Cotton said the homemade bombs are hidden along roadsides or near buildings and detonated by remote control or triggered when troops cross simple pressure plates.

"If only one strikes coalition forces, they have been successful," Cotton said. "It demonstrates to the world that the Taliban is still in the fight."

Four Canadian solders and one journalist, Calgary Herald reporter Michelle Lang, 34, were on their way home late in December when they were killed in a roadside bomb blast outside Kandahar. Their deaths came just one week after Lt. Andrew Nuttall, 30, was killed during a foot patrol outside the Afghan village of Nakhoney.

The Taliban were slower than Iraqi insurgents to adopt IEDs, but they are now the coalition's biggest threat.

In the "training lane" at this base in southern Afghanistan's Kandahar Province, civilian instructors teach Afghan infantry soldiers in what to look out for.

They are alerted to twists in roads, which force vehicles to slow down, making them easier to target. Something as innocuous as a rag on a wall or a pile of rocks can be used as a locator.

Cotton said that turning around the fight against IEDs will require a significant boost in the training and capabilities of the Afghan security forces. There is, for example, no police bomb squad in nearby Kandahar city, Afghanistan's second-largest and one of its most volatile.

Afghan police have been known to simply shoot at an IED once it has been located.

"At some point, we are going to be pulling out," he said. "But they are going to remain. They know much better than we do where to find them."

Pollock, 27, of Calgary, Alberta, said the Taliban are making more of an effort to reduce civilian deaths from IEDs because they are concerned that the population will turn against them.

The toll on civilians remains high, however.

In the last four months of 2009, 117 were killed by the devices, either deliberately or inadvertently, including 30 who died when a bus ran over an IED in September.

"Gradually they are going to have to take more responsibility," she said of the Afghan soldiers. "We are giving them exposure. We try to cover the most up-to-date threat."