According to the Pentagon, it briefly lost contact with two small US Navy boats operating in the Persian Gulf on Tuesday. The vessels have been picked up by Iran, who has assured Washington that both ships and crewmembers will be returned to the US "promptly."

"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 the Associated Press, adding that the ships were travelling between Kuwait and Bahrain when the Pentagon lost contact.

Senior defense officials told the Daily Beast the sailors — reportedly 9 men and one woman — would be held through US President Barack Obama's State of the Union address in Washington on Tuesday evening, and through Wednesday.

Military officials speaking to NBC News say that up to ten US sailors were on a training mission around noon ET when one of the vessels — small riverines — began experiencing mechanical difficulties and drifted into Iranian waters. The sailors have been detained by Iranian Revolutionary Guard forces on Farsi Island.

U.S. Naval Forces Central US Riverine Command Boats

The White House says it is working to resolve the situation, and wants all US personnel returned to normal deployment. Deputy national security adviser Ben Rhodes told reporters at the White House that the administration is hopeful that the situation will be resolved.

US Secretary of State John Kerry is in communication with Iranian counterpart Javad Zarif, and one senior official speaking to NBC says that Tehran believes the incident to be an accident and that the Americans will be released in international waters within hours.