“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 told the Spanish language television station Univision. “They obviously had mis-navigated … that’s how they believe they ended up in this circumstance.”

The Pentagon had previously contended that the boats strayed into Iranian waters because of mechanical problems.

Carter said that the sailors were not on “a covert mission”.

The boats were en route from Kuwait to Bahrain but ended up in Iranian waters.

“They did not report this navigational error at the time. It may be that they were trying to sort it out at the time they encountered Iranian boats. … We don’t know that fully yet,” the top defense official said.

The two boats with 10 sailors on board were held by Iranian Revolutionary Guards near Farsi Island on Tuesday before being released a day later.