The Red Sea and the nearby strategic Bab el-Mandeb strait, a crucial chokepoint for global shipping and crude oil, has been the scene of what the US describes as at least two missile attacks from rebel-held territory in Yemen.

The hostages, who were not identified, were transported from Yemen to neighboring Oman, the State Department said. The victims were taken to a hospital in Oman for treatment.

He said Omani authorities secured their release "in coordination with Yemeni parties in Sanaa", the capital which is under the control of the Shiite Huthi rebels and their allies, supporters of ousted president Ali Abdullah Saleh.

Yemen has been devastated by a war between government forces and those allied to the Houthi rebel movement.

Saudi Arabia, which supports Hadi's government, began conducting airstrikes in Yemen in March of 2015, when the conflict intensified. "Consular officers from the U.S. Embassy in Muscat stand ready to provide all possible consular assistance".

Last Monday, the USS Mason was passing through the Bab al-Mandeb Strait connecting the Red Sea to the Gulf of Aden.

The strike killed more than 140 people and wounded at least 525, sparking an worldwide outcry that prompted the coalition to announce an easing of an air blockade to allow the most seriously wounded to receive treatment overseas.

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Saturday's strike against USS Mason is the third that the ship suffered in a week.

The unidentified party insisted the site was "a legitimate military target", the English-language statement said.

But investigators said the coalition's air operations center ordered the attack "without obtaining approval from the Coalition command to support legitimacy and without following the Coalition command's precautionary measures to ensure that the location is not a civilian one that may not be targeted".

The coalition, which had initially denied any responsibility, said it accepts the results of the investigation and has started to implement the recommended changes.

Kerry, speaking to reporters in the Swiss city of Lausanne, also said that the United States was discussing a ceasefire in Yemen with Saudi officials.

There are initial unconfirmed reports of missiles possibly being fired from positions both ashore on Yemen and by small spotter boats operated by Houthi rebels. He added that United States was "very pleased" with the release.