Iranian military forces seized two U.S. Navy boats Tuesday and are detaining them on Iran’s Farsi Island in the Persian Gulf, senior U.S. officials told NBC News.

The 10 American sailors aboard the small riverine vessels were on a training mission around noon ET when one of the boats may have experienced mechanical failure and drifted into Iranian-claimed waters, officials said. Iran’s coast guard took them into custody.

The officials said it’s unclear whether the sailors — nine men and one woman — had strayed into Iranian territorial waters before they were captured.

American naval ships routinely navigate the waters of the Persian Gulf near Iranian territory. The Gulf has been a flashpoint in the Middle East, and the incident comes on the same day President Barack Obama was set to give his annual State of the Union address.