The Saudi and Yemeni governments both accuse Shia Iran of helping the Houthis, who belong to the Zaydi branch of Shia Islam.

ECONOMIST: Yemen's war

The Houthi movement, named after the tribe of its leader, says it represents the claims of Zaydi Shi'ite Muslims who ruled Yemen for over 1, 000 years.

MSN: Yemen security chief tells Iran to stop backing rebels

He is himself a Zaydi, whose adherents may account for more than a quarter of the country's 25m people, most of whom follow the Shafi school of Sunni Islam, one of its main four.

ECONOMIST: Yemen's war