Ten U.S. Navy sailors were detained on Tuesday by Iranian Revolutionary Guard forces when one of their boats apparently became disabled in the Persian Gulf.
A senior military official tells Fox News he's hopeful about the sailors being transferred Wednesday morning.
The offiicial also said that one of the sailors is female.
Pentagon officials said the incident occurred near Farsi Island in the Gulf. They said one of their two small boats had mechanical trouble, causing one or both to run aground. The sailors were then picked up by Iran and taken to the island. But it is unclear where they are now.
The boats were moving between Kuwait and Bahrain at the time, and the Pentagon briefly lost contact with the crews.
A senior Obama administration official told Fox News that Iranian authorities have assured the United States of the sailors' “safety and well-being” and said they “will promptly be allowed to continue their journey.”
The semi-official Iranian news agency, FARS, said the sailors were trespassing in Iranian waters.
The defense official also told Fox that one of the Navy riverine vessels “might” have been disabled and drifted into Iranian territorial waters, and the other stayed nearby attempting to fix the problem.
“Our top priority is the safety and security of our service members detained by Iran," said House Speaker Paul Ryan, R-Wis. "I am closely monitoring the situation, and I hope the president will soon update the American people."
President Obama reportedly will not address the incident in his State of the Union address on Tuesday night.
The incident comes amid heightened tensions with Iran, and only hours before President Obama was set to deliver his final State of the Union address to Congress and the public.
It set off a dramatic series of calls and meetings as U.S. officials tried to determine the exact status of the crew and reach out to Iranian leaders.
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, according to a senior U.S. official. Kerry "personally engaged with Zarif on this issue to try to get to this outcome," the official said.
Kerry learned of the incident around 12:30 p.m. EST as he and Defense Secretary Ash Carter were meeting their Filipino counterparts at the State Department, the official said.
This comes on the heels of an incident in late December when Iran launched a rocket test near U.S. warships and boats passing through the Strait of Hormuz.
The officials were not authorized to discuss the sensitive incident publicly so spoke on condition of anonymity.
The incident also takes place just days before Iran is expected to satisfy the terms of last summer's nuclear deal.
Once the U.N. nuclear agency confirms Iran's actions to roll back its program, the United States and other Western powers are obliged to suspend wide-ranging oil, trade and financial sanctions on Tehran. Kerry recently said the deal's implementation was days away.
Iran is testing the boundaries of this administration's resolve and they know the boundaries are pretty wide that the administration is willing to let them get away with many things," GOP presidential candidate and Florida Sen. Marco Rubio told Fox New's "Special Report with Bret Baier." "You're only seeing this accelerate since the deal was signed."
Fox News' Wes Barrett and Lucas Tomlinson and the Associated Press contributed to this report.