SEOUL (Reuters) – Rescue crews were forced to retreat from a stricken Iranian oil tanker in the East China Sea yesterday following an explosion on the ship as a fire raged for a fourth day after a dramatic collision. The blast happened on board the tanker in the afternoon after rescue crews were dousing the ship with foam in an attempt to put out the fire, China’s transport ministry said in a statement yesterday. The cause and damage to the tanker from the incident were not clear. The ship was carrying condensate, a highly flammable ultra-light crude, to deliver to South Korea when it collided with a Chinese freight ship on Saturday. Iran’s Navy joined the effort yesterday, a government official said.