'Lob bombs' new biggest worry for US in Baghdad

The 107 mm rockets that are used in the improvised bombs — which some call an airborne version of the roadside bombs that through the course of the war have been the leading killer of U.S. troops — are manufactured in Iran, officials said. But some officers cautioned against assuming Iran is directly involved.

The weapons are launched from small trucks and are fired in multiples of four to nine rockets at a time. The detonation is sometimes triggered by a signal from a cell phone, other times by a washing machine timer.