More than twice as many American soldiers have been killed in Iraq by roadside booby-traps than by sniper fire, mortars, car bombs, rocket-propelled grenades and suicide attackers combined, according to figures obtained by The Herald.

Of the 3003 US military deaths recorded as of December 30, 1080 died from wounds inflicted by blast and shrapnel from "improvised explosive devices", while 524 were victims of the other five confirmed forms of direct attack.

A further 203 died in road acidents and 81 in helicopter crashes. The casualty list classifies 618 deaths as "other causes", 50 in ambushes where there were more than one possible cause of death, and 447 as victims of unspecified "general hostile fire".

Despite a research budget of almost £3bn, the Pentagon has still to find failsafe methods of locating and neutralising roadside bombs as attacks on coalition vehicles continue at a rate of 1000 a month.

The booby-traps are also becoming more lethal, inflicting 67 out of the past 100 recorded kills of patrolling troops in Baghdad and the Sunni Triangle.

About half of the 23,000 US troops wounded since 2003 are also victims of what General Richard Cody, the US Army's vice-chief of staff, descibes as "the poor man's cruise missile".

British sources say insurgents looted enough explosives from army depots as Saddam's regime collapsed to maintain current levels of bomb-making "almost indefinitely".

In an attempt to reduce casualties, the Pentagon has recruited wounded veterans whose experience can be used in training tactics.

Although improved body armour and new frontline medical techniques have cut the number of potential fatalities by up to 50%, the downside of the blast effect of large explosions is that many survivors sustain brain damage or lose one or more limbs. More than 400 amputees are receiving specialist treatment.

Two British soldiers were injured when their patrol came under attack in southern Iraq.

A roadside bomb hit their convoy as they carried out a security patrol along the banks of a river in the Al Ashshar area of Basra province.

Violence continued in Iraq yesterday after a suicide car bomb struck a market in the Shi'ite district of Sadr City and police said 17 people died.

The attack occurred a day after a blast targeting students killed 70 in what appeared to be a renewed campaign of Sunni insurgent violence.

Yesterday's explosion near the outdoor Mereidi market also wounded 33 people.

Another suicide car bomb exploded earlier at a checkpoint in the northern oil city of Kirkuk, killing 10 people and injuring dozens.

Northern Iraq also has seen an increase in violence as Iraqi troops prepare for a crackdown in Baghdad.