REPUBLIKA.CO.ID, SANAA -- Saudi Arabia and Gulf region allies launched military operations including air strikes in Yemen on Thursday, officials said, to counter Iran-allied forces besieging the southern city of Aden where the U.S.-backed Yemeni president had taken refuge.

Gulf broadcaster al-Arabiya TV reported that the kingdom was contributing as many as 150,000 troops and 100 warplanes to the operations. Egypt, Jordan, Sudan and Pakistan were ready to take part in a ground offensive in Yemen, it said.

There was no immediate confirmation of those figures from Riyadh. Al-Arabiya also said the United Arab Emirates was sending 30 warplanes to join the operation, along with 15 each from Bahrain and Kuwait, 10 from Qatar, six each from Jordan and Morocco and three from Sudan.

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

The crisis now risks spiralling into a proxy war with Iran backing the Houthis, and Saudi Arabia and the other regional Sunni Muslim monarchies supporting Yemeni President Abd-Rabbu Mansour Hadi.

A widening Yemen conflict could also pose risks for global oil supplies, and Brent crude oil prices shot up nearly 6 percent soon after the operation began.

Unidentified warplanes had earlier launched air strikes on the main airport in the Yemeni capital, Sanaa, and its al Dulaimi military airbase, residents said.

A Reuters witness in the capital said four or five houses near Sanaa airport had been damage. 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.

The air strikes came soon after Saudi Arabia's ambassador in Washington, Adel al-Jubeir, announced the operation.

"We will do whatever it takes in order to protect the legitimate government of Yemen from falling," Jubeir told a news conference in Washington.

State media showed footage of Saudi jets taking off from a darkened airfield. It also showed Interior Minister Deputy Crown Prince Mohammed bin Nayef and Defence Minister Mohammed bin Salman - two of the most powerful royals after King Salman - touring a command facility together.

Fighting has spread across the Arabian peninsula country since last September, when the Houthis seized Sanaa and advanced into Sunni Muslim areas, forcing Hadi out of the capital.

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

The White House said in a statement late on Wednesday the United States supported the operation, led by the Arab Gulf Cooperation Council countries, and that President Barack Obama had authorized U.S. "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 militants from Tikrit.

Hadi has been holed up in Aden with loyalist forces since he fled Sanaa in February. Houthi rebels had overrun the airport in Aden on Wednesday, sparking concern about Hadi's whereabouts.

However, one of his aides said Hadi remains in his base in Aden and was "in high spirits" after the operation began. An Aden official later said Hadi loyalists had retaken the southern city's airport after heavy clashes.

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.

Houthi-run al-Masirah television reported that the Saudi-led air strikes had hit a residential neighbourhood north of Sanaa and caused dozens of casualties. It also urged medical personnel to report to hospitals in Sanaa immediately.

Al-Masirah footage showed the body of a girl and several of the wounded, including an unidentified man who wept as he said the air strikes had killed his son and destroyed his home.

It interviewed one witness who said: "We tell Saudi Arabia, don't you have enough with what's happening in Syria and Iraq.

You want to do the same in Yemen? Why are you hitting Yemeni civilians, women and children."

No independent verification of any casualties was immediately possible.

Although the news sparked jitters in the oil market, Asian importers said they were not immediately worried about supply disruptions.

Most oil tankers from Arab producers such as Saudi Arabia, the United Arab Emirates, Kuwait and Iraq have to pass Yemen's coastlines via the narrow Gulf of Aden in order to get through the Red Sea and Suez Canal to Europe.

The 40 km (25 mile)-wide strait between Yemen and Djibouti and the Strait of Hormuz between the Arabian peninsula and Iran are both considered chokepoints to global oil supplies by the U.S. Energy Information Administration.

"Just because Saudi and others conducted air strikes doesn't mean the oil market becomes suddenly tight," said Masaki Suematsu from brokerage Newedge Japan in Tokyo.

"But there will be repercussions ... If Saudi's oil facilities are attacked, the impact would be huge."

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