The death toll from a powerful explosion at Iran's biggest port of Bandar Abbas has risen to at least 25 dead, with more than 700 people injured, state media reported on Sunday, as firefighters worked to fully extinguish the fire.

The blast occurred as Iran began a third round of nuclear talks with the United States in Oman. The cause wasn't immediately clear.

At least five people have been killed and 700 injured in a massive explosion at one of Iran's key ports, state media is reporting. The suspected chemical blast took place at Shahid Rajaee, the country's largest commercial port, near the southern city of Bandar Abbas on Saturday morning.