The Saudi-led coalition battling Yemeni rebels said Saturday that one of its warplanes had "wrongly targeted" a funeral in the capital Sanaa, killing more than 140 people, and announced disciplinary measures.

The announcement came as an Omani aircraft evacuated from Sanaa more than 100 of the most seriously wounded in the October 8 strike, which injured at least 525 people and sparked international condemnation.

Muscat also said that it had mediated the release of two American citizens held in Yemen and flew them to Oman on Saturday night on the same relief flight.

US Secretary of State John Kerry welcomed the release but said it was too early to reveal their identities.

The team investigating the funeral raid said a coalition aircraft "wrongly targeted" the ceremony based on "incorrect information".

"Appropriate action... must be taken against those who caused the incident, and... compensation must be offered to the families of the victims," it said.

It also called on coalition commanders to change their procedures to prevent any repeat of the failings that led to the strike.

The coalition initially denied responsibility but ordered an investigation after Western condemnation, including from Saudi Arabia's closest allies.

A statement from the coalition said it accepted the results of the investigation and expressed "its regret at this unintentional incident and the ensuing pain for victims' families".

The strike was one of the deadliest in the coalition's 19-month-old bombing campaign in support of Yemen's beleaguered government.

More than 6,700 people have been killed in the impoverished Arabian Peninsula country since the coalition first intervened, nearly two-thirds of them civilians, according to the United Nations.

The alliance has come under increasing international scrutiny over civilian deaths.

Britain is to present a draft resolution to the UN Security Council next week calling for an immediate ceasefire in Yemen, after an earlier text condemning the funeral bombing was rejected by Russia as not strong enough.

- Wounded evacuated -

More than 300 people were critically wounded in the air raid, which targeted the funeral of the father of a senior Huthi official.

The outcry over the number of civilian casualties prompted the coalition to announce an easing of the air blockade it has enforced since March last year to allow the evacuation of the most seriously wounded for treatment abroad.

An Omani aircraft landed in the rebel-held Yemeni capital on Saturday and evacuated more than 111 of the most seriously wounded, a rebel official, Mohsen al-Dhaheri, said.

The rebels' deputy health minister Nasser Awjali told reporters more wounded wound be evacuated for treatment abroad.

Human Rights Watch said last week that the strike on the funeral was an "apparent war crime".

The inquiry team said that a party affiliated with Yemen's General Chief of Staff "wrongly passed information that there was a gathering of armed Huthi leaders in a known location in Sanaa, and insisted that the location be targeted immediately as a legitimate military target.

"The Air Operations Centre in Yemen directed a close air support mission to target the location... without following the coalition command's precautionary measures to ensure that the location is not a civilian one that may not be targeted," it concluded.

- Two Americans freed -

The relief flight also brought to Oman two US citizens who had been "held" in Yemen, the Oman News Agency said quoting a foreign ministry spokesman who said his country mediated their release.

The agency did not identify the pair but quoted the spokesman as saying Oman's mediation aimed "to help the American government obtain the liberation of a number of Americans held in Yemen."

The United States welcomed the release, with Kerry saying it was the fruit of much diplomatic effort.

"Their names are not being released at this point in time, but we're very pleased with that obviously and we're continuing to work on other hostage situations there and elsewhere," he said.

US State Department spokesman Mark Toner noted the "humanitarian gesture by the Huthis in releasing these US citizens".

There have been dozens of kidnappings of foreigners in Yemen over the years, most of them by members of the country's heavily armed tribes seeking concessions from the authorities.

Since the Huthi rebels overran the capital in September 2014, they have detained several Westerners, most of whom have been released through Omani mediation.

A member of the six-nation Gulf Cooperation Council, Oman has good ties with Yemen and is the only GCC country not to have joined the Saudi-led coalition.

The Omani aircraft also flew home Sanaa rebel negotiators who had been stranded in Muscat since the collapse of UN-brokered peace talks in Kuwait in August because of the air blockade, an AFP photographer reported.