The number of roadside bomb attacks in Afghanistan — and the casualties caused by those attacks — increased more than 30 percent during the past year, according to the International Security Assistance Force in Afghanistan.

According to the figures, bomb attacks have now become the largest single cause of NATO casualties in Afghanistan, reflecting a trend that began in the Iraq campaign.

Attacks targeting Afghan forces more than doubled, and attacks against civilians increased by 40 percent, officials said.

Improvised explosives "are the biggest threat we face," Maj. Gen. Jeffrey Schloesser, the U.S. commander in eastern Afghanistan, said in an interview with The Wall Street Journal. "They are the largest killer of ISAF troops."

Roadside bombs have grown in popularity among the Taliban and other militants fighting Western and Afghan forces. In Iraq, the bombs constantly evolved into more and more sophisticated weapons, causing nearly 2,000 U.S. deaths.

U.S. military officials have said they are seeing some of those bomb-making technologies make their way from the fight in Iraq to the fight in Afghanistan.

The military began a huge campaign against the roadside bomb threat, taking actions that ranged from creating a Pentagon-level anti-bomb task force to buying thousands of Mine Resistant Ambush Protected vehicles that offered more armor and protection to troops.

In Afghanistan, a resurgence of violence has cause the U.S. military to pledge some 30,000 extra troops in an escalation that is to build up during the coming year. At least one brigade of the troops has arrived and more are on their way, Pentagon officials have said.

The extra troops would effectively double the number of U.S. troops in the country.

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