The war began with US and Israeli attacks on 28 February, prompting Iran to attack Israel and US targets and allies in the Gulf.
In June, the US and Iran signed a ceasefire agreement, aimed at facilitating talks to end it.
Earlier this week, three commercial tankers were attacked as they tried to cross a US-recommended route through Omani waters. Iran has repeatedly said the only “safe” route is a separate route through its waters.
The incident prompted a series of US strikes in which 17 people were killed and 115 injured, according to Iranian officials. Iran responded with strikes on US allies in the Gulf.
The exchange raised tensions and prompted Trump to declare the ceasefire over.
However, the US leader said talks would continue and mediators have tried to revive the process.
US officials say they have conveyed through mediators the demand that Iran publicly state that the Strait of Hormuz, a vital international shipping route, is open and pledge to stop firing on commercial ships.
According to US media, Iran told American officials the attacks on tankers were a mistake and blamed a rogue internal group.
