The number of U.S. troops killed by roadside bombs in Afghanistan soared by 60 percent last year, while the number of those wounded almost tripled, new U.S. military statistics show.

All told, 268 U.S. troops were killed by the improvised explosive devices, or IEDs, in 2010, about as many as in the three previous years combined, according to the figures, obtained by The Washington Post. More than 3,360 troops were injured, an increase of 178 percent over the year before.

Military officials said an increase in attacks was expected, given the surge in U.S. and NATO troops, as well as the intensified combat. Even so, the spike comes despite a fresh wave of war-zone countermeasures, including mine-clearing machines, fertilizer-sniffing dogs and blimps with sophisticated spy cameras.

The U.S. military has struggled for years to find an antidote to the homemade explosives. IEDs - concocted primarily of fertilizer and lacking metal or electronic parts that would make them easier to detect - are the largest single cause of casualties for U.S. troops, by a wide margin.

Army Lt. Gen. Michael L. Oates, the director of a Pentagon agency dedicated to combating the bombs, noted that the percentage of IED attacks that have inflicted casualties - on U.S., NATO and Afghan forces, as well as Afghan civilians - has actually declined in recent months, from 25 percent last summer to 16 percent in December, according to U.S. military statistics.

"My main concern is driving these effective attacks down," he said. "We're enjoying success there, and I do believe we're going to continue to reduce [the enemy's] effectiveness."

Oates and other military officials have emphasized figures showing that IEDs killed fewer troops in the NATO-led coalition last year than in 2009 - a slight decline, from 447 to 430.

A further examination of those numbers, however, shows that casualty rates among U.S. troops have skyrocketed as they have taken over responsibility from European allies for fighting in southern Afghanistan, where resistance from insurgents has been most fierce. Meanwhile, casualty rates among allies have dropped.

Afghan insurgents planted 14,661 IEDs last year, a 62 percent increase over 2009 and more than three times as many as the year before.

Army Col. George B. Shuplinkov, chief of counter-IED programs for U.S. and NATO troops in Afghanistan, said he is guardedly optimistic that the number of bombs has crested, after reaching a "high-water mark" last summer.

"I think this [past] year we stopped the momentum," he said in a telephone interview. "We will know next spring. If it starts spiking back up in May or June, we'll have to reassess."

Oates predicted that the overall number of bomb attacks will not increase significantly this year. But he said it is unrealistic to expect the military to eliminate the threat as long as the Afghan insurgency persists.