The Iran-backed Houthi militia are reinforcing their positions around the strategically vital Bab al-Mandab Strait, dpa has learned.
A source close to the forces of the internationally recognized government said the rebels were digging trenches to defend territory recently seized along Yemen's Red Sea coast.
The Houthis overran the entire western coast of Yemen in a lightning offensive last week, capturing strategically located islands.
They now have virtually unrestricted access to the Bab al-Mandab strait, which connects the Red Sea with the Gulf of Aden. The world's most important shipping route between Europe and Asia passes through this waterway.
In normal times, around 10% of global maritime trade and 30% of global container traffic passes through the strait.
Traffic through the strait fell significantly after the militia started to attack ships in 2023, in its response to Israel's war on Gaza. Many shipping companies opted for the long and expensive detour via the Cape of Good Hope off the coast of South Africa.
Saudi Arabia, the world's leading oil exporter, is attempting to ship some of its oil via the Red Sea, as it has to be rerouted due to the blockade of the Strait of Hormuz connected with the Iran war.
Yemen's internationally recognized government and its allies, Saudi Arabia and various militias, are fighting a civil war against the Houthis.
The Houthis, who have controlled the capital Sanaa and other areas for years, are now on the advance. According to the United Nations, nearly 100,000 people have been displaced by the fighting.