JIM LEHRER: The death of six more Americans in Afghanistan focused new attention today on the dangers confronting U.S. forces there, chief among them, the bombs known as IEDs.
Ray Suarez has our report.
RAY SUAREZ: As of today, 66 U.S. troops have been killed in Afghanistan in July, with one more day left to go. The previous high was 60 killed in June. Another 20 troopers from other NATO countries have also been killed. That's actually down from 42 in June.
And, as fighting peaks in the sweltering Afghan summer, a familiar weapon is posing grave danger to U.S. forces, their international and Afghan partners and civilians. This American soldier had stepped on an improvised explosive device, or IED for short. Whatever it's called, the makeshift roadside bombs now cause 60 percent of coalition deaths in Afghanistan.
Specialist Bradly Parrish gave a sense of the threat he and others face.
SPC. BRADLY PARRISH, U.S. Army: Pretty scary, because you never know when it's coming. I mean, like when we go on patrols and we're walking, because they use the pressure plates out here, any step could potentially be your last, and you just kind of have to accept it.
RAY SUAREZ: The IED first became a killer in Iraq, as insurgents there made use of Iraqi munitions left littered across the country after the fall of Saddam Hussein.
The U.S. military tried to counter the bombs' devastating effect by deploying new, more heavily-armored vehicles and developed technologies to detect and defuse the bombs.
In Afghanistan, the improvised bombs are more often made of fertilizer, using agricultural-grade ammonium nitrate. Earlier this year, "Frontline" showed how the Taliban makes bombs. They can explode with enough force to flip a 15-ton MRAP vehicle.
International forces routinely discover huge caches of fertilizer used to create the weapons. All of this comes against the backdrop of 76,000 U.S. military documents being leaked this week by the Web site WikiLeaks. The group says it's reviewing 15,000 more records.
Yesterday, the chairman of the Joint Chiefs of Staff bluntly assessed the harm he thinks WikiLeaks and its founder, Julian Assange, have caused.
ADMIRAL MICHAEL MULLEN, Joints Chiefs chairman: Mr. Assange can say whatever he likes about the greater good he thinks he and his source are doing, but the truth is they might already have on their hands the blood of some young soldier or that of an Afghan family.
RAY SUAREZ: Pentagon leaders have ordered new security measures to safeguard information. As for safeguarding the troops, a U.S. military task force has so far spent billions of dollars to counter the continuing threat of roadside bombs.