Warplanes from Saudi Arabia and Arab allies struck Shia Muslim rebels fighting to oust Yemen's president on Thursday, a gamble by the world's top oil exporter to check Iranian influence in its backyard without direct military backing from Washington.

Riyadh's rival Iran denounced the assault on the Houthi militia group, which it backs, and made clear the kingdom's deployment of a Sunni coalition against Shia enemies would complicate efforts to end a conflict likely to inflame the sectarian animosities fuelling wars around the Middle East.

Warplanes bombed the main airport and the nearby al Dulaimi military air base of the Houthi-held capital Sanaa, residents said, in an apparent attempt to weaken the Houthis' air power and ability to fire missiles.

A Reuters witness in the capital said four or five houses near Sanaa airport had been damaged. Rescue workers put the death toll from the air strikes at 13, including a doctor who had been pulled from the rubble of a damaged clinic.

Yemen's crisis now risks spiralling into a major war with Iran backing the Houthis, and Sunni Muslim monarchies in the Gulf supporting Yemeni President Abed Rabbo Mansour Hadi and his fellow Sunni loyalists in Yemen's south.

Saudi Arabian Ambassador to the United States Adel Al-Jubeir says his country 'will do anything necessary' to protect the people of Yemen and 'the legitimate government of Yemen.' (Carolyn Kaster/Associated Press) "We will do whatever it takes in order to protect the legitimate government of Yemen from falling," Saudi Arabia's ambassador to the United States, Adel al-Jubeir, told a news conference in Washington.

In Aden, a local official reported that fighters loyal to Hadi retook the airport, a day after it was captured by forces allied to the Houthis advancing on the city. The facility remains closed and flights are cancelled.

Saudi-owned al-Arabiya TV reported that the kingdom was contributing 100 warplanes to the operation — dubbed "Storm of Resolve" — and more than 85 more were provided by the United Arab Emirates, Qatar, Bahrain, Kuwait, Jordan, Morocco and Sudan.

Egypt, Jordan, Sudan and Pakistan were ready to take part in a ground offensive in Yemen, the channel said.

A Saudi official familiar with defence matters told Reuters that a "land offensive might be needed to restore order."

Meanwhile, Iran's Foreign Ministry on Tuesday demanded an immediate halt to the "aggression and air strikes" in Yemen, the semi-official Fars news agency reported on Thursday.

"Military actions in Yemen, which faces a domestic crisis ... will further complicate the situation," Fars quoted Foreign Ministry spokeswoman Marzieh Afkham as saying.

A United Arab Emirates official expressed Gulf Arab concerns about Iranian influence in Yemen.

"The strategic change in the region benefits Iran and we cannot be silent about the fact that the Houthis carry their banner," UAE Minister of State for Foreign Affairs Anwar Mohammed Gargash wrote on Twitter.

The other Arab countries along with Pakistan reported to be willing to take part in the operation are also mostly Sunni.

Saud al-Sarhan, director of research at King Faisal Centre for Research and Islamic Studies in Riyadh: "It is a clear message on the 'Saudi defence doctrine'. Security and stability in the Arabian Peninsula is a red line, and Saudi Arabia doesn't tolerate any attempt to destabilize the region."

President in 'high spirits'

Yemen's slide towards civil war has made it a crucial front in Saudi Arabia's rivalry with Tehran, which Riyadh accuses of stirring up sectarian strife throughout the region and in Yemen with its support for the Houthis. Iran publicly denies funding and training the Houthis.

Yemeni protesters march during a demonstration against Shia Houthi group in Sanaa, on Wednesday. (Abdu Mohammed Yahya Haydar/Anadolu Agency/Getty Images) Fighting has spread across Yemen since last September, when the Houthis seized Sanaa and began to fan out across the country, forcing Hadi out of the capital.

Ambassador Jubeir said the assaults had been launched in response to a direct request by Hadi, who supported Washington's campaign of drone strikes against al-Qaeda's Yemen branch.

The White House said the United States supported the operation, led by the Arab Gulf Cooperation Council countries, and that U.S. President Barack Obama had authorized "logistical and intelligence support".

U.S. forces were not involved in direct military action in Yemen, a National Security Council spokeswoman said.

The Saudi-led strikes in Yemen coincided with an escalation of American involvement in Iraq, where U.S. planes carried out air strikes to support the drive to oust Islamic State of Iraq and Syria militants from Tikrit.

Hadi has been holed up Aden with loyalist forces since he fled Houthi custody in February.

One of his aides said Hadi was "in high spirits" since the operation began. Reuters later reported that Hadi had left his refuge in Aden under Saudi protection and arrived in Saudi Arabia.

A senior leader of Yemen's Houthi movement said the Saudi air strikes amounted to aggression against his country and warned they would set off a "wide war" in the region.