Update: 2 US Navy boats held by Iran but will be returned
Pentagon spokesman Peter Cook told The Associated Press that the boats were moving between Kuwait and Bahrain when the U.S. lost contact with them.
"We have been in contact with Iran and have received assurances that the crew and the vessels will be returned promptly," Cook said.
U.S. officials said that the incident happened near Farsi Island, situated in the middle of the Persian Gulf. They say it stemmed from some type of mechanical trouble with one of the boats, causing them to run aground. The troops were picked up by Iran.
Secretary of State John Kerry, who has forged a personal relationship with Iranian Foreign Minister Mohammed Javad Zarif through three years of nuclear negotiations, called Zarif immediately on learning of the incident, according to a senior U.S. official.
Kerry "personally engaged with Zarif on this issue to try to get to this outcome," the official said.
Kerry learned of the incident around 12:30 p.m. EST as he and Defense Secretary Ash Carter were meeting their Filipino counterparts at the State Department, the official said.