MIAMI (Reuters) – The 10 U.S. sailors who were held by Iran before being released on Wednesday made a navigational mistake that led them into Iranian waters but did not communicate that to Navy commanders before being intercepted, the U.S. military said on Thursday.

U.S. Defense Secretary Ash Carter said the information came from debriefings of the sailors, who were flown on Wednesday to a U.S. military facility in Qatar after Iran released them along with their two riverine boats.

“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 television’s Jorge Ramos, which will also air on Spanish-language Univision.

Carter’s comments were the most detailed so far from American officials on the incident, which rattled nerves just before the expected implementation of a landmark nuclear deal between Iran and world powers.

Diplomats in Washington and Tehran, through a series of anxious phone calls, sought to resolve the incident quickly, ensuring it did not torpedo the nuclear accord.

In the end, Iran released the U.S. sailors – nine men and one woman – on Wednesday.

The speedy resolution of the incident contrasted with previous cases in which British servicemen were held considerably longer, in one case nearly two weeks.

Carter said the sailors apparently did not radio in to tell their commanders they were off-course before encountering the Iranians.

“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 the Iranian boats and discovered they were inside of the territorial waters of Iran,” Carter said in the interview, which took place in Miami.

He denied that the sailors were on a covert mission, saying instead, “they were simply transiting from one place to another.”

One U.S. official, speaking on condition of anonymity, said it was clear that the boats did not run out of fuel.

A senior Navy official said the Navy was beginning the process of reintegrating the sailors after thorough medical, psychological and mental health examinations.

Navy officials were also staying in close touch with the families of the sailors to keep them apprised of the situation, the official said.

(Reporting by Phil Stewart; additional reporting by Andrea Shalal; Writing by Susan Heavey and Phil Stewart; Editing by Bernadette Baum and Dan Grebler)