Iran has released 10 US sailors held for entering its territorial waters, in a swift resolution of an incident that tested newly improved US-Iranian ties, reports BBC.The US expressed its gratitude to Iran for freeing the sailors one day after they were detained when their vessel broke down in the Gulf.Iranian state media said the group was released after apologising.It comes at a sensitive time, as the US and Iran try to implement the deal on Iran`s nuclear activities.The incursion was "unintentional", a statement from the Revolutionary Guards quoted by state media said.Earlier, the naval commander of the Guards, Gen Ali Fadavi, said investigations found a navigational failure was to blame."We have concluded that passage of Americans in our territorial waters was not a hostile passage or for espionage or similar acts," he told Iranian television.The US is investigating how the sailors entered Iranian waters.US Secretary of State John Kerry said he wanted to "express my gratitude to Iranian authorities for their co-operation in swiftly resolving this matter"."That this issue was resolved peacefully and efficiently is a testament to the critical role diplomacy plays in keeping our country safe, secure, and strong," Mr Kerry said in a statement.