Images of sailors held in Iran anger US

AAP
The US sailors who were held by Iran made a navigational mistake that led them into Iranian waters.

The US government has sought to defuse diplomatic tensions with Iran over the detention of two US Navy vessels by Iranian forces, but has complained about video released of the incident.

US Defence Secretary Ashton Carter said the US was investigating the detention and was "very glad" to have the sailors back.

The 10 sailors were released after 16 hours in Iranian custody. A video of the nine men and one woman kneeling with their hands over their heads prompted complaints, especially from Republicans who have spoken out against the Obama administration's move toward improving ties with Tehran and the Iran nuclear deal signed by Tehran in July with six world powers.

Carter reiterated US discontent with Iran's use of the video.

"Obviously, I don't like to see our people being detained by a foreign military," Carter said at a news conference on Thursday, but he said he wanted to know "the full context" of the incident.

"What you're looking through in those (video images) is the lens of the Iranian media," he said.

The sailors should be given an opportunity to explain what happened, Carter said.

US officials previously said a "navigational error" had caused the two vessels to drift into Iranian waters, but Carter said on Thursday there appeared to have been a combination of factors.

He said the Pentagon was still talking with the crew about what happened, but said the sailors were "clearly out of the position that they intended to be in".

The incident occurred as a key stage in the Iran-nuclear deal approaches.

State Department spokesman John Kirby said on Thursday he did not know when the so-called implementation day would come, but it was imminent.

"It will occur, and it will occur very soon," he said.

Kirby confirmed concrete had been poured into a nuclear reactor that was slated for decommissioning under the pact.

Once Iran fulfils this and other commitments under the deal, select sanctions are to be lifted.

Kirby said he wanted to give the sailors a chance to describe the circumstances of their capture, but said it was inappropriate for Iran to use the video of the sailors for propaganda purposes.

He noted the sailors were returned in less than 24 hours and all were safe without a shot being fired.

Iranian Foreign Minister Mohammad Javad Zarif tweeted that he was glad dialogue and respect resulted in the quick release of the US sailors.