US naval officials were on Wednesday investigating navigational error as the possible cause of an international incident that saw Iran briefly detain 10 sailors after they strayed into Iranian waters.

Contrary to initial reports, US officials are now ruling out any mechanical fault aboard the sailors' two small patrol boats, which were apprehended by Iran's Revolutionary Guards while en route from Kuwait to Bahrain.

"It's possible to make a navigational error of that type, it happens to everyone once in a while," a senior US naval official told AFP, speaking on condition of anonymity.

"Sometimes you get out of channel, sometimes you hit a buoy. ... Sometimes the charts aren't right."

Iran's Admiral Ali Fadavi, the naval commander of the Guards, said an investigation established that "this trespassing was not hostile or for spying purposes."

Instead "a broken navigation system" had led them astray, he said.

The sailors -- nine men and a woman -- were taken to Farsi Island after their two Navy patrol boats entered Iranian territorial waters late Tuesday.

The sailors were released Wednesday after being held overnight. They were allowed to leave Farsi Island aboard their two Riverine Command Boats, and were then taken to the nearby USS Anzio for a full debrief.

US and Iranian officials had scrambled to defuse the situation, which unfolded as Iran prepares to finally implement a nuclear deal with world powers aimed at ending the Islamic republic's long international isolation.

Iran said the sailors were released only after the United States had apologized, but US officials quickly denied that.

"Absolutely ZERO truth to rumors that @JohnKerry apologized to Iran over Sailors. Nothing to apologize for," John Kirby, spokesman for Secretary of State John Kerry, wrote on Twitter.

Kerry did, however, thank Iran for resolving the dispute quickly.

"There are always situations (that) have an ability if not properly guided to get out of control. And I'm appreciative for the quick and appropriate response of the Iranian authorities," Kerry said.

"This kind of issue was able to be peacefully resolved and officially resolved, and that is testament to the critical role diplomacy plays in keeping our country safe, secure, and strong," he added.

Video footage showed the Navy personnel with their hands on their heads as they were apprehended, and Iranian troops picking through an array of weapons found aboard their boats.

Other footage showed them eating a meal and drinking water, some smiling, while sitting on Persian rugs.