Vessels have been warned of the risks of underwater mines off Yemen.

The US Office of Naval Intelligence (ONI) said merchant shipping should beware travelling in the Bab el Mandeb strait.

Bombs have reportedly been placed outside the port of Mokha by rebel Houthi forces, who feared the area would be used for an airdrop of supplies.

The Yemeni army has pledged to act quickly to clear the devices, a report in the Asharq Al-Awsat daily said.

ONI noted that the closure of the 25km waterway would lead to substantial increases in total energy costs and global oil prices.

Houthis