Houthi rebels have captured several islands in the Red Sea and the Bab al-Mandeb Strait in an offensive that has roiled energy markets and cemented the Yemeni group’s control over the vital shipping artery. The Iranian-backed militants took over Perim Island, which splits the strait in two, as well as Zuqar and Hanish islands in the Red Sea, after a blitz along Yemen’s western coast and the capture of Mocha port on Thursday, according to Yemeni analysts.

“Now they are fully in control of Bab al-Mandeb,” said Ahmed Nagi, a Yemen analyst at Crisis Group. “The moment they took Mocha, they took over all the islands facing Mocha.” Mohammed Albasha, founder of the US-based risk advisory company Basha Report, said there were indications that the anti-Houthi coalition of Saudi-backed Yemeni factions “is crumbling” and “faces an uphill battle to counter the rebel offensive”.

The Houthi offensive dealt a significant blow to Saudi Arabia and the Yemeni government forces it backs, while boosting Iran’s efforts to push up energy prices as part of its battle with the US. Brent crude was trading under $105 a barrel on Friday after earlier climbing to almost $110.

The Bab al-Mandeb has become a vital route for Saudi oil exports since Iran throttled shipping through the Strait of Hormuz after the US and Israel launched their war against the Islamic republic in February.