KABUL, Afghanistan — Four American soldiers were killed by a roadside explosion in eastern Afghanistan on Monday, making July the deadliest month for American service members in the country since the 2001 invasion and underscoring the frightening rise in the sophistication and accuracy of roadside bombs.
With the four newest fatalities, at least 30 Americans have died in the first three weeks of July, surpassing the highest previous monthly toll, 28, reached in June 2008.
Part of the reason for July’s sharply higher fatalities — for American troops and for British and other NATO forces — is the three-week-old offensive in opium-rich Helmand Province, where United States Marines and British soldiers are trying to take control of areas dominated by the Taliban.
But the most significant factor is the increasing power of roadside bombs employed by guerrillas in eastern and southern Afghanistan, including Helmand.
The bombs are generally not as powerful as the improvised explosive devices, or I.E.D.’s, used by Iraqi guerrillas, who drew on huge stockpiles of artillery shells the Pentagon left unguarded. In later years, Shiite insurgents also employed explosively formed penetrators, a more precisely machined bomb that launched a fist-size molten ball that could pierce the thickest armor.
By contrast, Afghan guerrillas have fewer tools at their disposal — yet the toll of I.E.D. deaths continues to rise just as it did as the Iraqi insurgency grew stronger in 2005.
Twenty-one American soldiers have died from I.E.D. blasts so far this month, according to data recorded by icasualties.org, which tracks military deaths. Six more Americans were killed by fire from Kalashnikovs or other guns, rockets, mortar shells and rocket-propelled grenades. Two Air Force officers were killed when their F-15E fighter jet crashed on Saturday, and a sailor died from pneumonia earlier this month, according to the group’s Web site.
The military tallies do not include Afghan civilians regularly killed by I.E.D.’s often intended for Western or Afghan forces. On Sunday at least 10 Afghan civilians died in Farah Province along the Iranian border when a minibus and truck were struck by two hidden bombs, authorities said. “The Taliban are planting mines on roads in which both officials and civilians are traveling, but often civilians are the victims,” said Lt. Col. Juma Khan, an Afghan commander in Farah.
Taliban fighters do have access to mortar shells and military munitions, but many bombs are made from rudimentary ingredients like fertilizer and diesel fuel. Such bombs are less effective, but with enough fertilizer and diesel, Afghan guerrillas have shown they can destroy almost anything American forces operate in the rugged countryside.
And the Taliban exploit environmental factors: Afghanistan has few paved roads, making it easier for insurgents to bury bombs with no trace. Moreover, the new mine-resistant vehicles effective at protecting troops from I.E.D.’s in Iraq have struggled on Afghanistan’s uneven and craggy landscape. The Pentagon is developing a lighter and less cumbersome version.
Even before Monday’s American fatalities crossed a new threshold, July had already become the deadliest month for the entire NATO-led coalition: At least 56 coalition troops have died this month, surpassing the previous high of 46 recorded in June and August 2008, according to icasualties.org. Two out of every three coalition deaths in July have been from I.E.D.’s.
The British military has lost 17 soldiers this month, all but one in Helmand Province. Lt. Col. Rupert Thorneloe, the 39-year-old commander of the First Battalion of the Welsh Guards, was killed by an I.E.D. on July 1, the most senior British commander to die in battle since the Falklands war.
Taimoor Shah contributed reporting from Kandahar.
