Yemen’s Iran-backed Houthis have sent radio warnings to ships about their Saudi blockade, industry body the International Chamber of Shipping (ICS) said on Wednesday, as data analysed by AFP showed some vessels reversed course after the embargo.

On Monday, the Houthis announced a maritime embargo of Saudi Arabia, escalating the US-Iran war and threatening global oil markets by trying to hamper the top petrol exporter’s ability to bypass the Strait of Hormuz and reach the world.

“We can confirm that the Houthis were recorded transmitting a warning message to ships in the region,” the ICS said.

Christopher Long, the intelligence director at international risk management and maritime security company Neptune P2P Group, had earlier told AFP that the message “was recorded… by a ship in the Bab el Mandeb Strait” on Monday.

It went as follows: “’Yemeni naval force calling you on channel 1-6, according to the decision of Yemeni armed forces in the date of July 2-0, 2-0-2-6, including prevent navigation to Saudi ships because of the constant siege to Yemeni nation, so we warn all ships belonging to Saudi enemy to proceed via the Red Sea and Gulf of Aden, in case of non-compliance of Yemeni armed forces decision, those ships will be in our target, over.”

The Houthis did not say how they would enforce their blockade and have so far not attacked any ships.

Nine ships made a U-turn after the rebels announced their naval blockade, though some have resumed course, data analysed on Wednesday by AFP showed.

Before changing trajectories, the two vessels were signalling destinations in Qinzhou and Tianjin in China, and another in New Mangalore in India.

All three reversed course on Tuesday as they headed south toward Bab el-Mandeb. One of them, however, turned around again a few hours later and on Wednesday was continuing its journey towards the strait.

‘Individual risk assessment’

The other six vessels were on the opposite side of the strategic passage, in the Gulf of Aden or the Arabian Sea, when they turned back.

They comprise two container ships, a vehicle carrier, a loaded bulk carrier and two tankers, one of which was transporting a cargo from the United Arab Emirates. Three of these ships have since resumed their route toward Bab el-Mandeb.

If enforced, the embargo could further strain Saudi Arabia’s economy by cutting off access to its Red Sea ports, which have been vital for oil exports as renewed fighting limits passage through the Strait of Hormuz.

But despite Houthi threats and course changes, traffic continues in the Bab el-Mandeb Strait.

“Any vessel diversions that have occurred since the announcement of the Houthi blockade were made via individual risk assessment,” the ICS said, noting that the UK Maritime Trade Operations agency had “not yet seen a decisive change in traffic frequency through the Bab al-Mandeb”.

Forty-four vessels passed through the strait on July 20, the day the blockade was announced, and 29 the following day, according to Kpler.

Over the five preceding days, the maximum number of daily transits was 53, and the minimum was 30.

Saudi seaborne crude exports via the Bab el-Mandeb strait surged eightfold between March and mid-July 2026 compared with the same period in 2025, according to data from maritime tracker Kpler.

It skyrocketed to nearly 100 million barrels for the month of June, compared to 7 million barrels in February.

After the war started, Yanbu port in the Red Sea became crucial to Saudi seaborne crude exports.

In April and May, all of Saudi seaborne crude exports departed from Yanbu port, according to Kpler data. It represented 92 per cent of all seaborne crude exports in June and 78 per cent so far in July.