U.S. Defense Secretary Ash Carter said a navigation error -- not equipment malfunctions -- caused the crews of two Navy boats to stray into Iranian waters, where they were detained overnight by Iran and released.
"The information that they have given us, and through their commanders, is that they did stray accidentally into Iranian waters due to a navigation error," Carter said in an interview with Fusion network in Miami on January 14.
"They did not report this navigational error" to Navy commanders at the time the incident occurred on January 12, Carter added.
"It may be that they were trying to sort it out at the time they encountered Iranian boats... e don't know that fully yet," he said.
The day of the incident, U.S. officials had said mechanical problems had caused the boats to stray into Iranian waters. That was given by the United States as the reason that it did not need to apologize for the incident as demanded by Iran, since the crew could not be blamed for equipment failures.
But defense officials now say the central cause for the crews' entering Iranian waters was the navigational slip, which apparently was caused by human error rather than by an equipment malfunction.
The navigation error was compounded by some sort of engine trouble aboard one of the boats, defense officials said. The engine problem did not cause the boats to go off course but apparently prevented them from evading the Iranians once the crews realized they were inside Iran's territorial waters.
The boats, known as riverine command boats, were not on a covert mission and were simply making their way from Kuwait to Bahrain, Carter said.
The 10 U.S. sailors who were detained are now back with their American fleet and are getting debriefed and undergoing what the military calls "reintegration," a series of interviews and physical and mental health examinations to ease their return to duty. A Navy investigation will follow.
General Lloyd Austin, head of U.S. Central Command, said the equipment on the boats is being inventoried but nothing at first look appeared to be missing.
Iranian state television has released footage of the arrest, showing the sailors as they knelt down with their hands behind their heads and their two vessels being surrounded by several Iranian military fast boats.
It also released footage of one of the detained men, identified as a U.S. Navy commander, apologizing for the incident.
Carter acknowledged that the images made him feel uncomfortable, but he urged against a rush to judgment.
"Obviously, I don't like to see our people being detained by a foreign military," Carter told a news conference at Central Command in Tampa. "I think we need to give these guys the opportunity to tell us what was really going on and what the overall context [was]."
With reporting by Reuters and AP