Yemen’s Houthi movement said on Tuesday that it had forced several ships to change course in the Red Sea after threatening vessels linked to Saudi Arabia.

The Houthi-run Saba news agency said six ships in the Red Sea had been forced to alter their routes after receiving warnings from the group.

Three Houthi officials also said they had warned international shipping companies not to transit through the Bab al-Mandab Strait, the southern gateway to the Red Sea at the entrance to the Arabian Peninsula.

In an email sent to shipping companies, the Houthis said vessels were prohibited from loading or unloading cargo at Saudi ports, warning that any company involved in such activity could be targeted “anywhere”.

The announcement came a day after the Houthis declared a maritime shipping ban on Saudi Arabia. The move could open a new front against the United States in its conflict with Iran and increase risks to global energy supplies and trade outside the Gulf.