As the British government demanded the immediate release of 15 of its sailors whose boats were seized by Iranian naval vessels in the Persian Gulf on Friday, U.S. News has learned that this is not the first showdown that coalition forces have had with the Iranian military.

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.

During a joint border patrol, both American and Iraqi soldiers saw two Iranian soldiers run from Iraq back across the Iranian border as they approached. The patrol then came upon a single Iranian soldier, on the Iraqi side of the border, who did not flee.

While the joint U.S.-Iraqi patrol was speaking with the soldier, according to the report, the patrol was "approached by a platoon-size element of Iranian soldiers." An Iranian border captain then told the U.S. and Iraqi soldiers that "if they tried to leave their location, the Iranians would fire upon them." During this conversation with the Iranian captain, Iranian forces began firing and continued when U.S. troops tried to withdraw.

Iraqi and American forces returned fire "to break contact and left the area to report the incident," the report noted. "The Iranian forces continued to fire indirect fire well into Iraq as Coalition Force soldiers withdrew; for reasons unknown at this time, the Iraqi Army forces remained behind."

No American soldiers were wounded in the incident.

It is possible that Iranians thought they were in Iranian territory, according to U.S. military officials. Such border confusions and disputes happen routinely.

In the British naval incident on Friday, Iran claimed it seized the vessels because they were in its territorial waters. U.S. military officials tell U.S. News that the Iranian forces very likely belong to the Iranian Revolutionary Guards, which tend to be far more aggressive than regular Iranian naval forces, which U.S. military officials routinely describe as "extremely professional."

Iranian and Iraqi forces continue to clash in Iraq. U.S. special operations forces have been tasked with nabbing Iranian members of the Revolutionary Guards' al-Quds Brigade, the foreign operations arm of the Iranian military, which also supports Hezbollah in Lebanon and Hamas in the Palestinian territories.

U.S. forces grabbed six Iranians with alleged ties to the Iranian Revolutionary Guards in the northern Iraqi city of Arbil in January, reportedly using stun bombs, seizing computers, and taking down an Iranian flag from the raided building's roof. Iran said the building was a consulate and the men were diplomats–and continues to demand their release. One of Iraq's most powerful Shiite politicians condemned the raid, calling it an attack on Iraq's sovereignty.

American forces may soon be getting further insight into recent Iranian attacks. Earlier this month, a former Iranian deputy defense minister who once commanded the Revolutionary Guards–and is thought to have considerable knowledge of Iran's national security network–left the country and is said to be cooperating with western intelligence agencies, sharing information on links between Iran and Hezbollah in south Lebanon, for example. Iranian officials said the official, Ali Rez Asgari, was kidnapped by western agents.

Shortly afterward, Iran threatened to retaliate in Europe for the supposed kidnapping, what it claims to be the most recent in a series of abductions in the past three months. According to the British Sunday Times, in the Revolutionary Guards' weekly newspaper this week, a columnist believed to have close ties to Iranian President Mahmoud Ahmadinejad wrote: "We've got the ability to capture a nice bunch of blue-eyed, blond-haired officers and feed them to our fighting cocks. Iran has enough people who can reach the heart of Europe and kidnap Americans and Israelis."