Lightning Houthi advance in Yemen may bring dangerous new dimension to Iran war

The Houthis' lightning advance across the southern reaches of the Tihamah – Yemen's arid coastal plain – appears to have taken most observers by surprise.

Until recently, the anti-Houthi coalition known as the National Resistance held significant territory along Yemen's Red Sea coast. In a matter of days, much of this has fallen to the Houthis.

According to some estimates, the Iranian-backed rebels have captured as much as 130km (81 miles) of the country's strategically important coastline.

It's the group's most impressive military coup for several years, proving that despite a civil war that has lasted 12 years, devastating Saudi air raids and attacks by American, Israeli and British forces, the Houthis remain a force to be reckoned with.

With their opponents stunned and demoralised, it's unlikely the Houthis will be dislodged any time soon.

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"Now that they are there, they're going to be entrenched," Hisham al-Omeisi, senior analyst at the Brussels-based European Institute of Peace, told the BBC. "And it's going to be a lot more costly to push them out."