The advance toward Bab al-Mandeb threatens a vital Saudi oil route and risks drawing Riyadh back into a Yemen war it has spent years trying to leave.

Riyadh is balancing pressure on the Houthis with efforts to keep Iran from widening the conflict, as attacks threaten Saudi energy exports through the Red Sea.

Taking control of the towns bordering the Bab al-Mandeb Strait deals a significant blow to Saudi Arabia, which has relied heavily on the key waterway to keep its exports afloat.