The US military confirmed Sunday that Iranian soldiers attacked American troops working with Iraqi border guards last year in a volatile province northeast of Baghdad, showing the recent capture of 15 British forces was not the first time Iranians have taken Western forces by surprise in Iraq. US News and World Report, citing a US Army report from Iraq, said American troops working with Iraqi border guards inside the frontier were attacked by a much larger Iranian military unit in September east of the Diyala province town of Balad Ruz, 70 kilometers northeast of Baghdad. The magazine reported that the Iranians were on the Iraqi side of the border when they fired at the Americans with rocket-propelled grenades and small arms. No Americans were hurt in the incident, but four Iraqi soldiers, an interpreter, and an Iraqi border policeman remain missing. The US military said the account was accurate, adding the Americans were only performing their duties and the incident could have been a result of confusion in the vast desert area along the border. "There is a lot of open terrain," military spokesman Lt. Col. Mike Donnelly said in an e-mail. "Visual sighting and happenstance encounters from a distance occur routinely." He said the American troops involved were training, advising and helping the Iraqi border police as they seek to gain control over their own security.