Top oil exporter Saudi Arabia plans to beef up security at its borders and around oil and industrial facilities, state news agency SPA reported on Thursday, citing a statement by Deputy Crown Prince Mohammed bin Nayef.

Prince Mohammed, who is also the interior minister, had stressed "strengthening all security measures on the borders of the kingdom and in all public utilities and around the oil and industrial facilities", at a meeting to review security developments in Yemen, SPA said.

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

Opec member Kuwait said earlier on Thursday it had raised security around its oil facilities inside and outside the country after the military operation in Yemen.

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 Shi'ite enemies would complicate efforts to end a conflict that will only inflame the sectarian hatreds already fuelling wars around the Middle East.

But a senior Iranian official ruled out military intervention.

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 Reuters witness said four or five houses had been damaged. Rescue workers put the death toll 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 Reuters.

On the northern outskirts of Aden, Houthis and army loyalists fought extended gun battles with militiamen loyal to Yemeni President Abd-Rabbu Mansour Hadi. Thirteen pro-Houthi fighters and three militiamen were killed, the militiamen said.

Meanwhile, An Al Arabiya TV report said Hadi had left Aden, where he had been holed up, for Egypt under Saudi protection to take part in an Arab summit.

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, the capital of Lahj province north of Aden which killed five pro-Houthi fighters and four militiamen.

Thousands of Houthi supporters gathered to condemn the air strikes at the historic gate to Sanaa's old city, waving the Houthi banner and chanting, "Death to America!"

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 Hadi and his fellow Sunni loyalists in Yemen's south.

"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 apprent 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.

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

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

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

A senior Iranian official told Reuters: "Iran will use all possible political ways to allay tension in Yemen. Military intervention is not an option for Tehran."

A UAE official expressed Gulf 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.

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 destabilise the region." - Reuters