From US News & World Report:

Iranians Had Showdown With U.S. Forces

According to a U.S. Army report out of Iraq obtained by U.S. News, American troops, acting as advisers for Iraqi border guards, were recently surrounded and attacked by a larger unit of Iranian soldiers, well within the border of Iraq.

The report highlights the details: A platoon of Iranian soldiers on the Iraqi side of the border fired rocket-propelled grenades and used small arms against a joint patrol of U.S. and Iraqi soldiers east of Balad Ruz. Four Iraqi Army soldiers, one interpreter, and one Iraqi border policeman remain unaccounted for after the September incident in eastern Diyala, 75 miles east of Baghdad.

What is interesting is that the news story says the incident occurred "well within the border of Iraq", yet looking at the Army report this is not at all clear. The report says it happened "near the Iran/Iraq border." To the question "Was it on the Iraq or Iranian side of the border?" the report says only that "The exact location is part of the ongoing investigation into this incident."