The Houthis have said their embargo is in retaliation for a Saudi blockade of ports and airports in Houthi-controlled north-western Yemen.

Saudi Arabia has condemned the allegation and has vowed to "take all necessary measures to protect its ships in accordance with international law".

Yemen has been devastated by a civil war since 2014, when the Houthis captured the capital of Sana'a from the government. The conflict escalated in 2015, after a Saudi-led coalition of Arab states intervened to try and restore the official government.

There has been an informal truce between the Houthis and Saudi Arabia since 2022. But last week, the Houthis launched missiles at an airport in south-western Saudi Arabia in response to air strikes on Sanaa's airport that they blamed on the kingdom.

The Houthis have previously caused severe disruption to the the 32km-wide (20-mile) Bab al-Mandab Strait.

Shortly after the Gaza war broke out in October 2023, the Houthis began attacking merchant vessels in the Red Sea and Gulf of Aden, saying they were acting in support of the Palestinians. These attacks led to four ships being sunk, one vessel seized, and nine crew members killed.

Since the closure of the Strait of Hormuz, Saudi Arabia has diverted more than 70% of its crude exports from the Gulf to the Red Sea port of Yanbu through an east-west pipeline.

About four million barrels per day have been shipped from Yanbu in recent weeks, compared with about 973,000 a year earlier, according to data from Kpler and maritime analytics platform Signal Ocean.