A narrow waterway at the mouth of Red Sea between Yemen and Djibouti has provided an escape route for a sizeable chunk of the Middle East’s oil. That lifeline is now looking increasingly shaky.

For weeks, Yemen’s Iran-backed Houthi rebels have threatened shipping in the Bab al-Mandeb Strait, attempting to open a new front in the war between Tehran and Washington, now in its seventh month. In the past 48 hours, the Houthis have tightened their grip on the shipping route.

Security analyst Wolfgang Pusztai told Al Jazeera the group now has “the real capability to shut down any maritime traffic through Bab al-Mandeb if they want to”.

Andreas Krieg of King’s College London said the Houthis are well placed to defend the island in the short term because they control nearby territory, but that Mayun would be difficult to defend against an amphibious assault over the longer term.

The Houthis have said general shipping in the Red Sea and Bab al-Mandeb is safe from attacks, except for vessels linked to Saudi Arabia. However, they have not kept their promise.

Before the US-Israeli strikes on Iran, about 20 million barrels of oil transited the Hormuz each day. Once that waterway closed, Saudi Arabia began re-routing crude along its East-to-West pipeline and unloading barrels at Red Sea port of Yanbu.

Saudi crude flows through Bab al-Mandeb “collapsed” to about 400,000 barrels per day in August due to the Houthi threat and are now even lower, Richard Bronze, co-founder of Energy Aspects, told CNN. To avoid the strait, many oil cargoes must take a far longer route to reach Asia, via the Suez Canal, around Africa and across the Indian Ocean — an epic voyage adding about a month to transit times and pushing up freight costs.