US-led coalition forces in Iraq have been locked in a battle of ingenuity and adaptation with the bomb-makers of the insurgency.
Improvised Explosive Devices (IEDs), or roadside bombs, are the insurgents' preferred method of attacking coalition troops.
Senior US General John Abizaid says they are the "single greatest source of our casualties and remain the enemy's most effective weapon".
According to sources quoted by the New York Times, the number of roadside bombs rose in July to the highest monthly total of the war.
'DAISY CHAIN' IED AMBUSH SCENARIO
IEDs are used in a range of scenarios by insurgents. This graphic shows one method employed against coalition forces.
1: Hidden insurgent with detonator watching the road
2: Coalition convoy
3: IEDs buried in grass verge linked by 'daisy chain' of wire
4: Anti-tank mine used as IED
IEDs killed 427 American soldiers in Iraq in 2005, and 227 this year, according to the Iraq Coalition Casualty Count website.
Research analyst Francois Boo, of GlobalSecurity.org, says insurgents are skilled at developing more sophisticated and more powerful devices as US troops improve their tactics to deal with them.
Many are made from leftover munitions and explosive materials. New technology and tactics are available to bomb-makers on the internet.
The US says sophisticated bomb-making material from Iran has been found in IEDs in Iraq.
Infrared devices - set off as a vehicle breaks the beam, like a burglar alarm - are believed to have been a response to US troops using equipment to jam devices triggered by mobile phones and other types of transmitters.
'No silver bullet'
Other tactics range from burying IEDs in roadside verges to disguising them in plaster of Paris, rubbish or dead animals. Bridges and underpasses on Iraq's roads provide places to plant devices.
In some circumstances, a moving bus or lorry has been used to slow military convoys alongside a series of planted devices, maximising the damage on detonation.
Patrols also face the threat of vehicles - everything from cars and lorries to donkey carts and ambulances - loaded with explosives and being used in attacks.
Two years ago, many attacks on coalition troops started with a roadside bomb - followed by insurgents opening fire on the crippled vehicle or convoy. Subsequently, the bombs have often been used as the main element of the attack.
The US military is investing millions of dollars in combating IEDs. Efforts have included improving armoured protection for vehicles and troops and better communication about new insurgent methods.
The US says it is producing results, with nearly half of IEDs found and disabled before they can be detonated. In the six months before March 2006, coalition forces found and cleared nearly 4,000 IEDs, uncovered more than 1,800 weapons caches and bomb-making plants, and killed or detained hundreds of insurgent fighters and bomb-makers.
Iraqi civilians, who already have to live with the threat of suicide bombers, are now becoming victims of IEDs.
Mr Boo says this is partly a result of the coalition troops' increased vigilance and partly due to a change in strategy by the insurgents.
Ten civilians died and 69 were wounded when two roadside bombs detonated in a busy market in the al-Shurja district of Baghdad on 8 August. A few days earlier, a bus carrying at least 23 Iraqi soldiers was destroyed by a roadside bomb on the road between Tikrit and Baiji.
There is no technical "silver bullet" to end the threat, says Mr Boo.
"Without an end to the insurgency and a political solution on the ground the IED threat is going to remain. It can only be mitigated."