Yemen's Houthis have captured Perim Island inside the Bab el-Mandeb Strait, giving the Iran-aligned movement a foothold in the middle of one of the world's most important shipping routes and dramatically raising the stakes of their offensive along Yemen's Red Sea coast.

The capture comes barely a day after Houthi forces seized the historic port city of Mocha and pushed south towards Dhubab. Yemeni government and Houthi officials have now confirmed that the group has taken Perim, also known as Mayun, while Yemeni government sources say Dhubab has also fallen.

The geography explains why this matters.

Perim is a small volcanic island sitting directly inside Bab el-Mandeb, the narrow passage connecting the Red Sea with the Gulf of Aden. At its narrowest, the strait is roughly 29 kilometres wide. Perim divides it into two shipping channels used by vessels travelling between Asia, the Middle East and Europe through the Suez Canal.

The Houthis are therefore no longer simply advancing towards Bab el-Mandeb. They now occupy an island inside it.

The advance has been remarkably fast. The Houthis pushed south along Yemen's Red Sea coast, captured Mocha, moved into Dhubab and then reached Perim. They have also taken positions on the Hanish Islands farther north. Together, these gains give the group a much stronger military position around vessels approaching and passing through the strait.

It does not mean the Houthis have physically closed Bab el-Mandeb. Commercial ships can still pass through, and Houthi political official Hazam al-Assad told the Associated Press there was “no need for international concern”. But the group has already demonstrated that it possesses missiles, drones and other weapons capable of threatening vessels at considerable distances. From territory immediately surrounding the shipping lanes, that threat becomes considerably harder to ignore.

The timing makes the situation even more dangerous.

On the opposite side of the Arabian Peninsula, shipping through the Strait of Hormuz has already been severely disrupted by the war involving Iran, the United States and Israel. Saudi Arabia has increasingly relied on its East-West pipeline to move crude across the kingdom to the Red Sea port of Yanbu, allowing oil exports to bypass Hormuz.

But tankers leaving Yanbu for Asian markets eventually have to pass through Bab el-Mandeb.

That means Saudi Arabia now faces pressure around both sides of the Arabian Peninsula. Iran has enormous leverage around Hormuz, while its Houthi allies have moved into one of the most strategically important positions around Bab el-Mandeb.

Saudi Arabia has begun responding. Houthi media reported Saudi airstrikes against the airport at Mocha following its capture, while Yemeni government forces are preparing counteroffensives aimed at recovering territory lost during the Houthi advance.

The wider war is also returning to Yemen with alarming speed. A UN-brokered truce in 2022 had largely frozen the country's major front lines after years of devastating fighting. The latest offensive is tearing that relative calm apart. More than 46,000 people have already fled the renewed fighting, according to the UN.

There is also growing scrutiny of Iran's role. Yemeni government, Iranian and regional sources have told Reuters that Iran's Revolutionary Guards provided direct guidance during the Houthi offensive down the Red Sea coast. Tehran denies exercising military command over the group.

For global markets, however, the immediate concern is simpler.

Bab el-Mandeb is one of the arteries connecting Asian manufacturing and Middle Eastern energy supplies with European markets. Disruption forces vessels to make the much longer journey around Africa's Cape of Good Hope, adding time and cost to global trade.

The Houthis may not have closed that artery.

But within days, they have captured Mocha, reached Dhubab and planted themselves on Perim Island inside the strait itself.