(RT) — Two small US craft in the Persian Gulf were taken in custody by Iran after they appeared in Iranian waters. The crews are to be released shortly, according to various US officials.

 “We have been in contact with Iran and have received assurances that the crew and the vessels will be returned promptly,”Pentagon spokesman Peter Cook told AP.

The crews, which total 10 Navy sailors, are being held at Farsi Island, a highly restricted island between Bahrain and Kuwait, where Iran has a naval base. US officials are saying it is unclear how the crew members ended up in Iranian waters, though Secretary of State John Kerry has kept phone contact with Iranian officials in Tehran, urging for a release. A senior official told NBC News the Iranians understand a mistake was made and have agreed to a release to come in hours.

According to AP, an anonymous senior official says Kerry “personally engaged with” Iranian Foreign Minister Javad Zarif to work out a solution almost immediately upon hearing of the development around 12:30 pm EST.

Josh Earnest, the White House spokesperson, said the sailors will be released “promptly” and ” allowed to continue their journey.”