Yemen's Houthi fighters have been accused of breaking the country's humanitarian ceasefire in its first 24 hours, as fighting continued between rival sides in several parts of the country.

"The Houthi militias have violated the truce," the Arab coalition led by Saudi Arabia said in a statement on Thursday carried by the official Saudi Press Agency.

The statement alleged 12 breaches of the ceasefire, along the Saudi-Yemen border and in Yemen itself.

The heaviest violence on the ground was in the southwestern province of Taiz, where the Houthis and their allies - forces loyal to ousted President Ali Abdullah Saleh - shelled residential areas.

Fighting was also reported in the southern city of Ad-Dali', as rebels fired tank shells, rockets and mortars against positions belonging to forces loyal to exiled President Abd-Rabbu Mansour Hadi.