Questions were raised in the United States Wednesday over the treatment of 10 US sailors who were held briefly by Iran after their boats drifted into Iranian waters in the Persian Gulf.

The military personnel and their two vessels were released and taken to an undisclosed location in the gulf after the incident was diffused, US news reports said.

Iranian authorities confirmed earlier in a statement that they had been released.

Both Iran and the United States said they had not been mistreated, but a video shown on Iranian television showed the sailors on the deck of their own boat with their hands over their heads in a pose that made it appear they were being taken prisoner.

Another image showed the sailors - nine men and one woman - sitting on a rug sharing a meal.

There also were questions over whether the United States had offered an apology.

In a short video one of the sailors apologizes, saying, "It was a mistake that was our fault and we apologize for our mistake."

That contrasted with how the incident was characterized in Washington, where US officials said no apology was offered. They said the boats had been in transit and had not intended to enter Iranian territory.

State Department spokesman Mark Toner said the video was being assessed and the initial conclusion was that the sailors were treated well.

The two US boats strayed 2 kilometres into Iranian waters on Tuesday and were detained by Iran's Revolutionary Guards.

Iran determined that the breach of its waters was not an act of espionage but instead was an accident due to the navigation equipment on the boats being broken.

The 10 sailors were brought to a safe place and treated well, Revolutionary Guard naval commander General Ali Fadawi said.

The foreign ministers of both countries, John Kerry and Mohammad Javad Zarif, had been in constant contact, speaking at least five calls during the course of the incident, a US official said.

Kerry said the situation could easily have gotten out of control, but praised Iranian authorities for the cooperation and quick response. He said the sailors had not been mistreated.

"We can all imagine how a similar situation might have played out three or four years ago," he said. "It is clear that today this kind of issue was able to be peacefully resolved and efficiently resolved, and that is a testament to the critical role that diplomacy plays in keeping our country safe, secure, and strong."

Iran and the United States had no diplomatic relations for more than 35 years but tensions have eased since a deal over Iran's nuclear ambitions in July. The two countries are also working together on peace talks to try to end the Syrian civil war.

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