Diplomats and U.N. staff flee Yemen as Houthis target Aden

Residents reported heavy clashes between the Houthis and mainly Sunni tribal fighters in the south of the country, while the air campaign sought to stall a fresh offensive by the Shi'ite Muslim group on Aden from the east.

Riyadh's intervention, a surprise move from a conservative monarchy better known for flexing its muscle in oil markets than through military might, is planned to last a month but could extend for five or six, a Gulf diplomatic source said.

He said satellite imagery had shown in January that the Houthis had repositioned long-range Scud missiles in the north, close to the Saudi border and aimed at Saudi territory. A Yemeni official said Iran, which says it has not armed the Houthis, was providing parts for the missiles.