Thailand and Cambodia exchanged heavy artillery fire for a second day on Friday as their worst fighting in over a decade intensified and spread to new areas, despite international calls for a ceasefire.

At least 16 people have been killed and tens of thousands displaced in the escalating border battle.

Both sides have blamed each other for starting the conflict and on Friday ratcheted up the rhetoric, with Thailand accusing Cambodia of deliberately targeting civilians and Cambodia alleging Thailand was using cluster munitions, a controversial and widely condemned ordnance.