(Islamabad, Pakistan) -- Pennsylvania's senior senator is calling for U.S. troops to be better protected against roadside bombs in the Middle East. Democrat Bob Casey is currently making his third trip to Islamabad, Pakistan, where he's meeting with Pakistani government officials. Casey says it's important to track transportation of the main ingredient of the improvised explosive devices, or IED's. "One of the basic problems is the ammonium nitrate, which most Americans know as fertilizer, the ammonium nitrate is coming into Afghanistan from Pakistan," Casey says. 125 U.S. troops have been killed by roadside bombs so far this year, and 78 Pennsylvanians have been killed in Afghanistan since combat began. Casey is Chairman of the Senate Foreign Relations Subcommittee on Near Eastern and South and Central Asian Affairs.