The United States carried out new strikes on southern Iran on Thursday, after President Donald Trump threatened to "finish the job" if Tehran did not agree to a peace deal.

Iranian media reported three loud explosions rang out in the port city of Bandar Abbas in the early hours of Thursday morning, following US strikes earlier in the week that underscored the fragile state of a diplomatic push to get a provisional peace agreement across the finish line.

"Today, US Central Command Forces shot down four Iranian one-way attack drones that posed a threat around the Strait of Hormuz," a US official, speaking on condition of anonymity, said in a statement to AFP.

"US forces also struck an Iranian ground control station in Bandar Abbas that was about to launch a fifth drone," the official said.

Even after earlier strikes on Monday night, Iran said on Wednesday a return to war was unlikely but that its military was nonetheless "lying in wait".

The mixed signals have thrown into question talks aimed at formally ending the war that began on 28 February with US-Israeli strikes on Iran.