The United States has seized an Iranian cargo ship in the middle of a fragile ceasefire, raising fresh doubts over whether tensions with Tehran are already escalating again.

With Iran rejecting further talks and instability returning to the Strait of Hormuz, the prospects for diplomacy and the truce itself are increasingly uncertain.

On The Big Story, Hongbin Jeong speaks with Dr Leon Goldsmith, Honorary Senior Lecturer in Middle East Politics at the University of Otago, on whether the ceasefire can hold and what this latest escalation means for regional stability and global energy markets.