But the U.S. officials focused mainly on a deadlier version of the improvised explosive device: the explosively formed penetrator.

NPR: U.S. Says Iran Supplying Weapons to Iraq Militias

The U.S. government believes the Islamic republic's Revolutionary Guard Corps' Quds Force has been training militias and providing weaponry, such as the explosively formed penetrator roadside bomb.

CNN: Iraqi leader heading back to Iran for security talks

Iran was the primary supplier of deadly EFP-IEDs (Explosively Formed Penetrator-Improvised Explosive Devices) to the insurgents in Iraq and operated training camps for those insurgents inside Iran.

CENTERFORSECURITYPOLICY: Misguided on Iran

This is especially worrisome since some of the research in question would explore whether a Robust Nuclear Earth Penetrator (RNEP) could be fashioned to penetrate deep underground before detonating.

CENTERFORSECURITYPOLICY: Empty words?

He recently admitted that his own country's new bunker-busting bomb, the Massive Ordnance Penetrator (MOP, pictured above being dropped from a B-52), needs an upgrade to take on the deepest Iranian bunkers.

ECONOMIST: Bunker-busting

The President thinks we need to design a Robust Nuclear Earth Penetrator capable of holding at risk the growing number of deeply buried sites used by North Korea, Iran and the like to conceal weapons of mass destruction and command-and-control facilities.

CENTERFORSECURITYPOLICY: Hobson��s choices (cont.)