TEHRAN, Young Journalists Club (YJC) -Mahdi Rezayi, who is the Fire Department deputy for operations in Mashhad, the capital of Khorasan Razavi Province, said the incident occurred at about 6 am local time (0130GMT) in a two-story building on Saturday.
The explosion caused three buildings to collapse while 15 more structures were damaged up to 60 percent, he said.
Hossein Heydari, the provincial deputy chief prosecutor, confirmed that the explosion of gas-fired water heater caused the incident, saying seven of the victims died instantly on the spot while four others succumbed to their injuries in hospital.
Many Iranians use gas-fired water heaters and similar cases in the past have been blamed on gas leakage from the heaters and a disregard for safety measures.
Source: Press TV