This story was written for CBSNews.com by CBS News correspondent Cami McCormick, who can be heard frequently on CBS Radio.
After warning that the threat of deadly EFPs, or , was growing at an alarming rate, the U.S. military now says there's been a "dramatic" decrease in the use of the powerful roadside bombs.
EFPs "can punch through most of the armor out on the battlefield today," Army Lt. Col. Christopher Garver, a U.S. military spokesman said of the devices, which U.S. officials have said come from Iran.
They are blamed for more than 170 American deaths since 2004, when they first appeared on the battlefield. More than 600 American troops have been wounded by the bombs. EFPs account for a small percentage of the roadside bombs in Iraq, but they are responsible for a disproportionately high number of casualties.
Garver says EFP attacks have dropped significantly since December.
"In February, we noticed a 47 percent decrease in explosively formed penetrators being detonated against our troops, a 53 percent decrease in the number of troops wounded and a 51 percent decrease in the number of troops killed" by the devices, he said.
The reported decrease came as the U.S. military offered to reporters what it said was proof that weapons like EFPs were being manufactured in Iran. The Iranian government has denied any involvement in providing weapons or material support to Iraq's insurgency.
According to Garver, the reasons for the marked drop in EFP incidents could include the detention of three Iranians in Baghdad in December. One of the men was believed to be a high-level Operations Officer with theof Iran's elite Revolutionary Guard.
Garver says the men were suspected of involvement with weapons smuggling.
Most EFP attacks have occurred in Baghdad, and another reason for their decrease may be the ramped-up presence of U.S. and Iraqi troops in the capital due to the ongoing security crackdown.
The city is surrounded by checkpoints, the most critical of which are to the south, according to American military commanders who believe most weapons find their way into Baghdad from that direction.
The next brigade of U.S. troops arriving in Iraq as part of President Bush's troop surge will headto help choke off those .
"We have to control what we call the belts, to the north, west and south. We're going to have troops in each of those areas, the south being a priority for the next group of troops coming in, to prevent weapons from coming back in once we've cleared them all out of Baghdad," Garver said.
Editor's Note: When first reporting this story on March 21, the numbers of EFP attacks on U.S. troops provided by the military showed a more dramatic drop. Lt. Col. Garver contacted Cami McCormick on March 22 to correct the figures he initially reported.
The numbers first reported were: 77 percent drop in incidents, 74 percent drop in deaths, and 64 percent drop in injuries involving EFPs.
Garver apologized for any confusion, and said the military was striving to convey accurate information. He added that the "first two weeks of March show the same trend" in decreased EFP incidents.