BAGHDAD, July 2 — Iranian operatives helped plan a January raid in Karbala in which five American soldiers were killed, an American military spokesman in Iraq said today.

Brig. Gen. Kevin J. Bergner, the military spokesman, also said that Iran’s Islamic Revolutionary Guard Corps has used operatives from the Lebanese militia group Hezbollah as a “proxy” to train and arm Shiite militants in Iraq.

American military officials have long asserted that the Quds Force, an elite unit of Iran’s Revolutionary Guard, has trained and equipped Shiite militants in Iraq. The Americans have also cited extensive intelligence indicating that Iran has supplied Shiite militants with the most lethal type of roadside bomb in Iraq, a bomb called the explosively formed penetrator, which is capable of piercing an armored vehicle.

Previously, Iranian officials have said that the United States is fabricating evidence to back up its accusation that Iran is sending bombs and weapons into Iraq. Some critics have cast doubt on the American military statements about the penetrator bombs, saying the evidence linking them to Iran was circumstantial and inferential.