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

Iran denounced the surprise assault on its proteges in the Houthi militia group and made clear Saudi Arabia's deployment of a Sunni coalition against its Shia enemies would complicate efforts to end a conflict that will only inflame the sectarian hatreds already fuelling wars around the Middle East.

The Saudi intervention marked a major escalation of the Yemen crisis, in which Iran backs the Houthis, and Sunni Muslim monarchies in the Gulf support President Abd-Rabbu Mansour Hadi and his fellow Sunni loyalists in Yemen's south.

In the capital Sanaa, which Houthi rebels trying to oust the president seized in September, warplanes bombed the main airport and the nearby al Dulaimi military air base, residents said, in an apparent attempt to weaken the Houthis' air power and ability to fire missiles.

A witness said four or five houses had been damaged. Rescue workers put the death toll from at 13, including a doctor pulled from the rubble of his clinic.

In a day of heavy fighting, warplanes struck Houthi fighters near Yemen's border with Saudi Arabia, tribal and Houthi sources told.

On the northern outskirts of Aden, Houthis and army loyalists fought extended gun battles with militiamen loyal to Hadi. 13 pro-Houthi fighters and 3 militiamen were killed, the militiamen said.

Fighters loyal to Hadi retook Aden 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 Arabia also cancelled flights to its southern airports.

There was also heavy street fighting in Houta, north of Aden, which killed 5 pro-Houthi fighters and 4 militiamen.

Thousands of Houthi supporters gathered to condemn the air strikes at the gate to Sanaa’s old city, waving Houthi banners and chanting, “Death to America!”

"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 an apparent reference to Iran, Saudi Foreign Minister Saud al-Faisal said the operation aimed to counter the "aggression of Houthi militias backed by regional powers".

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

Jordan and Sudan said their forces were involved in the operation. Egyptian air forces were participating, and four naval ships headed to secure the Gulf of Aden.

Pakistan was considering a request to send ground forces.