Iranian and coalition forces have had several skirmishes

According to a report in USNews, the recent skirmish between British sailors and Iranian forces is only the most recent confrontation between the Iranians and the coalition.

Exclusive: 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.

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