Dhaka, April 27 -- A massive explosion and fire at Iran's largest commercial port has killed at least four people and injured more than 500 others, authorities say."Unfortunately, at least four deaths have been confirmed by rescuers," Babak Mahmoudi, head of the Red Crescent Society's Relief and Rescue Organisation, said on the state television on Saturday.The Iranian state media reported that at least 516 people were injured at the explosion at Shahid Rajaei port, located more than 1,000km (620 miles) south of the capital, Tehran.Iranian state television said initial reports indicate negligence in the storage of flammable materials at the site, while Tehran Times reported that the explosion of several containers was the initial cause of th...