In a statement, the U.S. military also said the gang had sent "militants from Iraq to Iran for terrorist training."
It said the arrests were made today during a raid in Sadr City, a Shi'ite stronghold in east Baghdad.
The raid targeted militants allegedly smuggling weapons from Iran, including explosively formed penetrators (EFPs).
Those devices are capable of piercing armored vehicles. U.S. officials say at least 170 U.S. soldiers had been killed by EFPs since 2004.
Iran has previously denied U.S. allegations that it has aided and abetted insurgents in Iraq.
Iranian Shi'a protesting the Golden Mosque Bombing in Iraq on February 24
WHAT IS GOING ON? On March 8, RFE/RL's Washington office hosted a roundtable discussion on relations between Iraq and Iran. Although most analysts agree that Iran has been actively involved in Iraq since the U.S.-led military operation to oust former Iraqi President Saddam Hussein, they continue to debate the nature, extent, and intent of that involvement.
The RFE/RL briefing featured WAYNE WHITE, former deputy director of the U.S. State Department Bureau of Intelligence and Research's Office of Analysis for the Near East and South Asia, and A. WILLIAM SAMII, RFE/RL's regional analyst for Iran and editor of the "RFE/RL Iran Report."
LISTENListen to the complete RFE/RL briefing (about 75 minutes):
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