WASHINGTON - Saudi Arabia and its Gulf Arab allies launched air strikes in Yemen against Houthi fighters who have tightened their grip on the southern city of Aden where the country's president had taken refuge, the Saudi envoy to Washington said on Wednesday.

Saudi Ambassador to Washington Adel al-Jubeir told reporters a 10-country coalition had joined in the military campaign in a bid "to protect and defend the legitimate government" of Yemen President Abd-Rabbu Mansour Hadi.

He declined to give any information on Hadi's whereabouts, but said the president, who has fled his residence, was still running the government along with members of his Cabinet.

Jubeir said Iranian-backed Houthi Shi'ite militants were now in control of the Yemeni air force and of the country's ballistic weapons.

"This is a very dangerous situation and we must do everything we can to protect the people of Yemen and protect the legitimate government of Yemen," Jubeir told a news conference at the embassy.

He told reporters that Saudi Arabia had consulted with the United States but that Washington was not participating in the military operation.

A US official who asked not be named told Reuters that the United States was providing support to Saudi Arabia as it carries out its operation, but gave no details.

Jubeir said the operation, which was launched at 7 p.m. EDT (2300 GMT) on Wednesday in response to a request for assistance by Hadi, was not limited to one particular city or region.

"We have air assets from a number of countries in the (Saudi) kingdom and we have military assets that are on their way to the kingdom to participate in these operations," Jubeir said.

Jubeir did not name any of the countries involved in the 10-strong coalition but said it included Saudi Arabia's Gulf Arab allies.