The Pentagon says that Iran has detained two U.S. Navy boats, along with 10 naval personnel, but has told the United States that the crew will be returned "promptly."
Defense Department spokesman Peter Cook said the boats were moving between Kuwait and Bahrain on January 12 when U.S. officials 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.
The incident raised unexpected drama just hours before President Barack Obama was scheduled to give his annual State of the Union speech to a joint session of Congress.
U.S. officials told The Associated Press news agency one of the boats had some type of mechanical trouble that caused them to run aground and they were picked up by Iran.
"We subsequently have been in communication with Iranian authorities, who have informed us of the safety and well-being of our personnel," another U.S. defense official said. "We have received assurances the sailors will promptly be allowed to continue their journey."
In a statement carried by the ISNA news agency, the Islamic Revolutionary Guard Corps said 10 sailors in all were detained, including nine men and one woman. It said the sailors received "Islamic treatment" and that they were being kept at an "appropriate" location.
The statement said the boats were detained near Farsi Island in the Persian Gulf and transferred to the island, situated about midway between Iran and the coast of Saudi Arabia.
The hard-line Iranian news agency Fars, meanwhile, said the boats were detained after they "patrolled" Iranian territorial waters illegally and that their GPS would confirm their location.
Deputy national security adviser Ben Rhodes told reporters at the White House that the administration was working to resolve the situation and was hopeful about it.
Reuters quoted a senior U.S. administration official as saying that Iranian Foreign Minister Mohammad Javad Zarif told U.S. Secretary of State John Kerry on January 12 that U.S. sailors who ended up in Iranian custody would be allowed to continue their journey promptly.