Yemen’s Houthis have seized Mokha, Dhubab and strategic islands overlooking the Bab al-Mandeb Strait, putting pressure on a shipping route that has become increasingly important to Saudi Arabia as the war with Iran restricts traffic through the Strait of Hormuz.

The Iran-backed group reached Perim, also known as Mayyun, on Friday after Saudi-backed Yemeni government forces withdrew from the island, four government sources told Reuters. The Houthis took Dhubab, the last major coastal town before Bab al-Mandeb, a day after capturing the Red Sea port of Mokha. Yemeni officials told The National that the group had also taken Zuqar Island. 

The advances come as the Houthis are also striking Saudi territory directly and enforcing a blockade against Saudi-linked shipping in the Red Sea.

Perim, a 13-square-kilometer island between Yemen and Djibouti, sits inside Bab al-Mandeb and divides the strait into two shipping channels. The gains do not give the Houthis control over all shipping through the strait, which they could already threaten with missiles and drones from farther north.