Rebels fighting for the control of Yemen and forces backing President Abd-Rabbu Mansour Hadi have engaged in fierce clashes in the country's south, leaving more than 140 people dead in 24 hours, as the Red Cross faces delays to deliver vital supplies.

Monday's clashes happened in Aden, a power base for Hadi, who fled to Saudi Arabia as the rebels, known as Houthis, expanded their control across the country.

Citing unnamed officials, the AFP news agency reported that 17 civilians were among more than 140 people killed in Aden, where fighting continued as rebels tried to seize a port in the city.