Insurgents took the time and effort to tunnel underground and place an unusually large improvised explosive well below the surface, said David Small, spokesman for the counter-IED agency. They also had time to plan where to position themselves to remotely detonate the bomb, Small said.
Hel said other details about the attack are classified, but it is believed the insurgents had learned through observation that reduced coalition patrolling gave them more time to plan this attack.
Afghan forces are taking the brunt of insurgent violence this year as U.S. troops pull back from a combat role to a support mission in line with plans to end the American and coalition combat role by December 2014. Yet IED attacks are taking a relatively larger toll on the smaller force that is still operating there.
Deaths from IEDs alone from April through June represented 9 percent of all coalition casualties, including those wounded in action, Sweetser said. That compared to 7 percent in the same period in 2012.
Because U.S. and coalition troops are not as active beyond their bases as they had been previously, prior to the Afghans taking the lead combat role across the country, Taliban fighters “are coming to us and attacking us on our bases,” Sweetser said.
A spokesman for coalition forces in Kabul, Lt. Col. Will Griffin, acknowledged the increased lethality of some attacks but said, “We don’t necessarily identify that as a trend.” He said a “full spectrum” of tools designed to counter the threat of IEDs is still available to coalition troops even as they shift to a back-seat role.
U.S. officials also are now grappling with a time lag in learning details about IED attacks, since the Afghans are in the combat lead and use more rudimentary means of reporting up their chain of command, Sweetser said. He said it now can take many weeks, rather than several hours, to learn details of IED attacks.
There are now about 60,000 U.S. troops in Afghanistan, down from 87,000 a year ago. The number is scheduled to shrink to 34,000 by February.
President Barack Obama has yet to announce whether he intends to keep some number of American forces in Afghanistan after 2014 to train Afghans and to hunt extremists.