WASHINGTON (AP) — The Pentagon says the crew members of two small Navy craft are being held by Iran. But U.S. officials have been assured by Tehran that the crew and the vessels will be returned safely and promptly.

Officials say 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.

A Pentagon spokesman says the boats were moving between Kuwait and Bahrain when the U.S. lost contact with them.

A senior U.S. official says 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.

The official says Kerry "personally engaged with Zarif on this issue to try to get to this outcome."

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