Two American prisoners held captive by Yemen Houthi rebels have been released and taken to neighbouring Oman after Omani officials mediated their release, US Secretary of State John Kerry said on Saturday.

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.

He suggested he may have more to say on Sunday about ending the violence between Iran-backed Houthis and the Yemen government, which is supported by Gulf states.

A Saudi-led campaign in Yemen has come under severe criticism since an air strike a week ago on a funeral gathering in the Yemeni capital Sanaa that killed 140 people according to a UN estimate and 82 according to the Houthis.

U.S. Secretary of State John Kerry, left, and Saudi Arabia's Foreign Minister Adel al-Jubeir, right, attend a meeting where they discussed the crisis in Syria, in Lausanne, Switzerland, on Saturday

The hostages were flown to the capital of Oman, Muscat, above

The Americans' release was part of a complicated negotiation that saw those wounded in the funeral strike flown to Oman for treatment, and the Americans released to Muscat, Oman.

It's unclear how long they were held hostage or the circumstances under which they were kidnapped.

'An airplane flew from Muscat to Sanaa, it took the Houthi delegation back to Sanaa and it took wounded people from the funeral back to Oman - this is something we have been working on for the last days - and it also secured the release of two American citizens from the Houthi,' Kerry said.

Sam Farran, a former U.S. Marine, center, was greeted by family and supporters in September 2015 after being released by Houthi rebels after being held for six months with two other hostages

'Their names are not being released at this point in time, but we were very pleased with that and we continue to work on other hostage situations here and elsewhere.'

Oman state television broadcast footage of the two Americans disembarking from a plane belonging to the Royal Air Force of Oman. Yemenis wounded in the civil war in Yemen were also flown for treatment to Oman on the same plane, it reported.

A Foreign Ministry official told the broadcaster Oman had worked with Yemeni authorities in Sanaa to secure the Americans' release. A Houthi official confirmed their departure from Sanaa.

The Americans were kidnapped by the Houthi militant rebels (above) which have stepped up kidnappings in recent years to fund their activities and negotiate prisoner releases

Freelance journalist Casey Coombs (above) was held by Houthi rebels for two weeks

The US State Department expressed gratitude to the Omani government for facilitating the release and recognised the action as a 'humanitarian gesture' by the Houthis, the northern Yemeni armed group that seized control of the capital Sanaa in 2014.

'We are working very hard to get a framework in Yemen which will change the dynamics and move that to the table as soon as possible,' Kerry said, adding: 'I will maybe have more to say on that tomorrow (Sunday) in London but it remains a top priority for us to try to end the violence.'

The United Nations estimates that 10,000 people have been killed in the fighting in Yemen and blames coalition air strikes for 60 percent of some 3,800 civilian deaths since March 2015.

Oman, a U.S. ally which maintains warm relations with nearby Iran, has served as a mediator for past prisoner releases and other diplomatic initiatives.

Earlier this month, Oman was credited with helping to secure the release of a French-Tunisian woman working for the Red Cross who had been kidnapped by armed men in Yemen and held for nearly a year.

The country has seen increasing instability. In 2015, two American men, identified by the Wall Street Journal as Scott Darden of Transoceanic Development and Sam Farran of Universal Eagles for Security Services were released in Oman after being held by Houthi rebels in Yemen for six months.

American journalist Casey Coombs was also held for two weeks by the rebels, according to the New York Times. He had written for outlets such as The Intercept, The American Prospect and Time magazine.

In late September, an American English teacher was apparently taken hostage in Sanaa, according to the Associated Press, but it is unclear if this teacher is one of the Americans released.